The role of multi-drug resistance p-glycoprotein in glucocorticoid function: studies in animals and relevance in humans

Comparison of chemotherapy outcomes between normal and high serum cortisol concentration in dogs with lymphoma

BACKGROUND

Increased serum cortisol (COR) concentrations may induce glucocorticoid resistance by down-regulation of glucocorticoid receptor (GCR), resulting in decreased chemotherapy efficacy in dogs with lymphoma.

HYPOTHESIS

Investigate the relationship between serum COR concentrations and chemotherapy outcomes in dogs with lymphoma.

ANIMALS

Thirty client-owned dogs with lymphoma, with serum COR concentration measured using serum samples collected at diagnosis.

METHODS

Retrospective study. Dogs were divided into 2 groups based on serum COR concentrations: a normal group (n = 16) with COR concentrations <6 μg/dL and a high group (14) with COR concentrations ≥6 μg/dL. We compared signalment, clinical signs, stage, type of lymphoma, adrenal gland size, alkaline phosphatase (ALP) activity, response to chemotherapy, progression-free survival (PFS), overall survival (OS), and rate of P-glycoprotein (P-gp)- and GCR-positive cells between the 2 groups.

RESULTS

No significant differences were found in the demographic characteristics between the 2 groups. However, the high COR group exhibited a significantly lower response to chemotherapy, PFS, and OS compared with the normal COR group. Serum ALP activity was significantly higher in the high COR group than in the normal COR group. Adrenal gland size was also significantly larger in the high COR group. Although no significant differences were found in the rate of P-gp-positive cells between the 2 groups, the rate of GCR-positive cells was significantly lower in the high COR group.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our data suggests that measurement of serum COR concentrations may serve as a potential prognostic factor and evaluation index.

P-Glycoprotein Exacerbates Brain Injury Following Experimental Cerebral Ischemia by Promoting Proinflammatory Microglia Activation

Microglia are activated following cerebral ischemic insult. P-glycoprotein (P-gp) is an efflux transporter on microvascular endothelial cells and upregulated after cerebral ischemia. This study evaluated the effects and possible mechanisms of P-gp on microglial polarization/activation in mice after ischemic stroke. P-gp-specific siRNA and adeno-associated virus (p-AAV) were used to silence and overexpress P-gp, respectively. Middle cerebral artery occlusion/reperfusion (MCAO/R) and oxygen-glucose deprivation/reoxygenation (OGD/R) were performed in mice and cerebral microvascular endothelial cells (bEnd.3) in vitro, respectively. OGD/R-injured bEnd.3 cells were cocultured with mouse microglial cells (BV2) in Transwell. Influences on acute ischemic stroke outcome, the expression of inflammatory cytokines, and chemokines and chemokines receptors, microglial polarization, glucocorticoid receptor (GR) nuclear translocation, and GR-mediated mRNA decay (GMD) activation were evaluated via reverse transcription real-time polymerase chain reaction, western blot, or immunofluorescence. Silencing P-gp markedly alleviated experimental ischemia injury as indicated by reduced cerebral infarct size, improved neurological deficits, and reduced the expression of interleukin-6 (IL-6) and IL-12 expression. Silencing P-gp also mitigated proinflammatory microglial polarization and the expression of C-C motif chemokine ligand 2 (CCL2) and its receptor CCR2 expression, whereas promoted anti-inflammatory microglia polarization. Additionally, P-gp silencing promoted GR nuclear translocation and the expression of GMD relative proteins in endothelial cells. Conversely, overexpressing P-gp via p-AAV transfection offset all these effects. Furthermore, silencing endothelial GR counteracted all effects mediated by silencing or overexpressing P-gp. Elevated P-gp expression aggravated inflammatory response and brain damage after ischemic stroke by augmenting proinflammatory microglial polarization in association with increased endothelial CCL2 release due to GMD inhibition by P-gp.

High-order framework nucleic acid for targeted-delivery of antisense peptide nucleic acids to overcome drug resistance

A sophisticated high-order framework nucleic acid (FNA) was engineered for the targeted delivery and responsive release of environment tolerant antisense peptide nucleic acids (asPNAs). The dendritic FNA-asPNAs system was constructed via simple one-pot modular assembly and demonstrated a good synergistic effect with chemotherapy on drug resistant cancer cells.

The ATP-binding cassette proteins ABCB1 and ABCC1 as modulators of glucocorticoid action

Responses to hormones that act through nuclear receptors are controlled by modulating hormone concentrations not only in the circulation but also within target tissues. The role of enzymes that amplify or reduce local hormone concentrations is well established for glucocorticoid and other lipophilic hormones; moreover, transmembrane transporters have proven critical in determining tissue responses to thyroid hormones. However, there has been less consideration of the role of transmembrane transport for steroid hormones. ATP-binding cassette (ABC) proteins were first shown to influence the accumulation of glucocorticoids in cells almost three decades ago, but observations over the past 10 years suggest that differential transport propensities of both exogenous and endogenous glucocorticoids by ABCB1 and ABCC1 transporters provide a mechanism whereby different tissues are preferentially sensitive to different steroids. This Review summarizes this evidence and the new insights provided for the physiology and pharmacology of glucocorticoid action, including new approaches to glucocorticoid replacement.

Generalized and tissue specific glucocorticoid resistance

Glucocorticoids (GCs) are steroid hormones that influence several physiologic functions and are among the most frequently prescribed drugs worldwide. Resistance to GCs has been observed in the context of the familial generalized GC resistance (Chrousos' syndrome) or tissue specific GC resistance in chronic inflammatory states. In this review, we have summarized the major factors that influence individual glucocorticoid sensitivity/resistance. The fine-tuning of GC action is determined in a tissue-specific fashion that includes the combination of different GC receptor promoters, translation initiation sites, splice isoforms, interacting proteins, post-translational modifications, and alternative mechanisms of signal transduction.

The Role of Stress in Bipolar Disorder

Stress is a major risk factor for bipolar disorder. Even though we do not completely understand how stress increases the risk for the onset and poorer course of bipolar disorder, knowledge of stress physiology is rapidly evolving. Following stress, stress hormones - including (nor)adrenaline and corticosteroid - reach the brain and change neuronal function in a time-, region-, and receptor-dependent manner. Stress has direct consequences for a range of cognitive functions which are time-dependent. Directly after stress, emotional processing is increased at the cost of higher brain functions. In the aftermath of stress, the reverse is seen, i.e., increased executive function and contextualization of information. In bipolar disorder, basal corticosteroid levels (under non-stressed conditions) are generally found to be increased with blunted responses in response to experimental stress. Moreover, patients who have bipolar disorder generally show impaired brain function, including reward processing. There is some evidence for a causal role of (dysfunction of) the stress system in the etiology of bipolar disorder and their effects on brain system functionality. However, longitudinal studies investigating the functionality of the stress systems in conjunction with detailed information on the development and course of bipolar disorder are vital to understand in detail how stress increases the risk for bipolar disorder.

Pharmacodynamic mechanisms of anti-inflammatory drugs on the chemosensitization of multidrug-resistant cancers and the pharmacogenetics effectiveness

Drug resistance as a remarkable issue in cancer treatment is associated with inflammation which occurs through complex chemical reactions in the tumor microenvironment. Recent studies have implicated that glucocorticoids and NSAIDs are mainly useful combinations for inflammatory response modulation in chemotherapeutic protocols for cancer treatment. Immunosuppressive actions of glucocorticoids and NSAIDs are mainly mediated by the transrepression or activation regulation of inflammatory genes with different DNA-bound transcription factors including AP-1, NFAT, NF-κB, STAT and also, varying functions of COX enzymes in cancer cells. Interestingly, many investigations have proved the benefits of these anti-inflammatory agents in the quenching of multidrug resistance pathways. Numerous analyses on the ABC transporter promoters showed conserved nucleotide sequences with several DNA response elements that participate in transcriptional regulation. Furthermore, genetic variations in nucleotide sequences of membrane transporters were strongly associated with changes in these transporters' expression or function and a substantial impact on systemic drug exposure and toxicity. It appeared that several polymorphisms in MDR transporter genes especially MDR1 have influenced the regulatory mechanisms and explained differences in glucocorticoid responses.

Therapeutic Applications of Genes and Gene-Engineered Mesenchymal Stem Cells for Femoral Head Necrosis

Osteonecrosis of the femoral head (ONFH) is a common and disabling joint disease. Although there is no clear consensus on the complex pathogenic mechanism of ONFH, trauma, abuse of glucocorticoids, and alcoholism are implicated in its etiology. The therapeutic strategies are still limited, and the clinical outcomes are not satisfactory. Mesenchymal stem cells (MSCs) have been shown to exert a positive impact on ONFH in preclinical experiments and clinical trials. The beneficial properties of MSCs are due, at least in part, to their ability to home to the injured tissue, secretion of paracrine signaling molecules, and multipotentiality. Nevertheless, the regenerative capacity of transplanted cells is impaired by the hostile environment of necrotic tissue in vivo, limiting their clinical efficacy. Recently, genetic engineering has been introduced as an attractive strategy to improve the regenerative properties of MSCs in the treatment of early-stage ONFH. This review summarizes the function of several genes used in the engineering of MSCs for the treatment of ONFH. Further, current challenges and future perspectives of genetic manipulation of MSCs are discussed. The notion of genetically engineered MSCs functioning as a "factory" that can produce a significant amount of multipotent and patient-specific therapeutic product is emphasized.

Role of P-glycoprotein on CD69+CD4+ cells in the pathogenesis of proliferative lupus nephritis and non-responsiveness to immunosuppressive therapy

Introduction

P-glycoprotein (P-gp) expression on activated lymphocytes in systemic lupus erythematosus (SLE) plays a role in active efflux of intracellular drugs, resulting in drug resistance. The role of P-gp-expressing lymphocytes in the pathogenesis of SLE remains unclear. The aim of this study was to determine the importance of P-gp⁺CD4⁺ cells in organ manifestations in refractory SLE.

Methods

The proportion of P-gp⁺CD4⁺ cells was determined by flow cytometry in peripheral blood of patients with SLE (n=116) and healthy adults (n=10). Renal biopsy specimens were examined by immunohistochemistry for P-gp expression.

Results

CD69 is a marker of CD4 cell activation. The proportion of both P-gp-expressing CD4⁺ cells and CD69-expressing CD4⁺ cells in peripheral blood was higher in SLE than control. The proportion of P-gp⁺CD69⁺CD4⁺ cells correlated with Systemic Lupus Erythematosus Disease Activity Index and was higher in poor responders to corticosteroids. Furthermore, the proportion of P-gp⁺CD69⁺CD4⁺ cells was significantly higher in proliferative lupus nephritis (LN) with poor response to corticosteroids. The efficacy of immunosuppressive therapy depended on the regulation of the proportion of P-gp⁺CD69⁺CD4⁺ cells. Marked accumulation of P-gp⁺CD4⁺ cells in renal interstitial tissue and high proportion of peripheral P-gp⁺CD69⁺CD4⁺ cells were noted in patients with proliferative LN.

Conclusions

The results showed high proportion of P-gp⁺CD69⁺CD4⁺ cells in peripheral blood and their accumulation in renal tissue in patients with proliferative LN refractory to CS therapy, suggesting that P-gp expression on activated CD4⁺ T cells is a potentially useful marker for refractoriness to treatment and a novel target for treatment.

Glucocorticoids and Reproduction: Traffic Control on the Road to Reproduction

Glucocorticoids are steroid hormones that regulate diverse cellular functions and are essential to facilitate normal physiology. However, stress-induced levels of glucocorticoids result in several pathologies including profound reproductive dysfunction. Compelling new evidence indicates that glucocorticoids are crucial to the establishment and maintenance of reproductive function. The fertility-promoting or -inhibiting activity of glucocorticoids depends on timing, dose, and glucocorticoid responsiveness within a given tissue, which is mediated by the glucocorticoid receptor (GR). The GR gene and protein are subject to cellular processing, contributing to signaling diversity and providing a mechanism by which both physiological and stress-induced levels of glucocorticoids function in a cell-specific manner. Understanding how glucocorticoids regulate fertility and infertility may lead to novel approaches to the regulation of reproductive function.

MANAGEMENT OF ENDOCRINE DISEASE: Epidemiology, quality of life and complications of primary adrenal insufficiency: a review

In this article, we review published studies covering epidemiology, natural course and mortality in primary adrenal insufficiency (PAI) or Addison's disease. Autoimmune PAI is a rare disease with a prevalence of 100-220 per million inhabitants. It occurs as part of an autoimmune polyendocrine syndrome in more than half of the cases. The patients experience impaired quality of life, reduced parity and increased risk of preterm delivery. Following a conventional glucocorticoid replacement regimen leads to a reduction in bone mineral density and an increase in the prevalence of fractures. Registry studies indicate increased mortality, especially evident in patients diagnosed with PAI at a young age and in patients with the rare disease autoimmune polyendocrine syndrome type-1. Most notably, unnecessary deaths still occur because of adrenal crises. All these data imply the need to improve the therapy and care of patients with PAI.

Antidepressant Potential of Chlorogenic Acid-Enriched Extract from Eucommia ulmoides Oliver Bark with Neuron Protection and Promotion of Serotonin Release through Enhancing Synapsin I Expression

Eucommia ulmoides Oliver (E. ulmoides) is a traditional Chinese medicine with many beneficial effects, used as a tonic medicine in China and other countries. Chlorogenic acid (CGA) is an important compound in E. ulmoides with neuroprotective, cognition improvement and other pharmacological effects. However, it is unknown whether chlorogenic acid-enriched Eucommia ulmoides Oliver bark has antidepressant potential through neuron protection, serotonin release promotion and penetration of blood-cerebrospinal fluid barrier. In the present study, we demonstrated that CGA could stimulate axon and dendrite growth and promote serotonin release through enhancing synapsin I expression in the cells of fetal rat raphe neurons in vitro. More importantly, CGA-enriched extract of E. ulmoides (EUWE) at 200 and 400 mg/kg/day orally administered for 7 days showed antidepressant-like effects in the tail suspension test of KM mice. Furthermore, we also found CGA could be detected in the the cerebrospinal fluid of the rats orally treated with EUWE and reach the level of pharmacological effect for neuroprotection by UHPLC-ESI-MS/MS. The findings indicate CGA is able to cross the blood-cerebrospinal fluid barrier to exhibit its neuron protection and promotion of serotonin release through enhancing synapsin I expression. This is the first report of the effect of CGA on promoting 5-HT release through enhancing synapsin I expression and CGA-enriched EUWE has antidepressant-like effect in vivo. EUWE may be developed as the natural drugs for the treatment of depression.

Determinants and significance of corticosterone regulation in the songbird brain

Songbirds exhibit significant adult neuroplasticity that, together with other neural specializations, makes them an important model system for neurobiological studies. A large body of work also points to the songbird brain as a significant target of steroid hormones, including corticosterone (CORT), the primary avian glucocorticoid. Whereas CORT positively signals the brain for many functions, excess CORT may interfere with natural neuroplasticity. Consequently, mechanisms may exist to locally regulate CORT levels in brain to ensure optimal concentrations. However, most studies in songbirds measure plasma CORT as a proxy for levels at target tissues. In this paper, we review literature concerning circulating CORT and its effects on behavior in songbirds, and discuss recent work suggesting that brain CORT levels are regulated independently of changes in adrenal secretion. We review possible mechanisms for CORT regulation in the avian brain, including corticosteroid-binding globulins, p-glycoprotein activity in the blood-brain barrier and CORT metabolism by the 11ß hydroxysteroid dehydrogenases. Data supporting a role for CORT regulation within the songbird brain have only recently begun to emerge, suggesting that this is an avenue for important future research.

Disease control by regulation of P-glycoprotein on lymphocytes in patients with rheumatoid arthritis

The main purpose of treatment of rheumatoid arthritis (RA) with disease modifying antirheumatic drugs (DMARDs) is to control activation of lymphocytes, although some patients do not respond adequately to such treatment. Among various mechanisms of multidrug resistance, P-glycoprotein (P-gp), a member of ATP-binding cassette transporters, causes drug-resistance by efflux of intracellular drugs. Certain stimuli, such as tumor necrosis factor-α, activate lymphocytes and induce P-gp expression on lymphocytes, as evident in active RA. Studies from our laboratories showed spontaneous nuclear accumulation of human Y-box-binding protein-1, a multidrug resistance 1 transcription factor, in unstimulated lymphocytes, and surface overexpression of P-gp on peripheral lymphocytes of RA patients with high disease activity. The significant correlation between P-gp expression level and RA disease activity is associated with active efflux of drugs from the lymphocyte cytoplasm and in drug-resistance. However, the use of biological agents that reduce P-gp expression as well as P-gp antagonists (e.g., cyclosporine) can successfully reduce the efflux of corticosteroids from lymphocytes in vitro, suggesting that both types of drugs can be used to overcome drug-resistance and improve clinical outcome. We conclude that lymphocytes activated by various stimuli in RA patients with highly active disease acquire P-gp-mediated multidrug resistance against corticosteroids and probably some DMARDs, which are substrates of P-gp. Inhibition/reduction of P-gp could overcome such drug resistance. Expression of P-gp on lymphocytes is a promising marker of drug resistance and a suitable therapeutic target to prevent drug resistance in patients with active RA.

DHEAS and cortisol/DHEAS-ratio in recurrent depression: State, or trait predicting 10-year recurrence?

BACKGROUND

Major depressive disorder (MDD) has been associated with low dehydroepiandrosterone-sulphate (DHEAS), - particularly relative to high cortisol - although conflicting findings exist. Moreover, it is unclear whether low DHEAS is only present during the depressive state, or manifests as a trait that may reflect vulnerability for recurrence. Therefore, we longitudinally tested whether low DHEAS and high cortisol/DHEAS-ratio in recurrent MDD (I) reflects a trait, and/or (II) varies with depressive state. In addition, we tested associations with (III) previous MDD-episodes, (IV) prospective recurrence, and (V) effects of cognitive therapy.

METHODS

At study-entry, we cross-sectionally compared morning and evening salivary DHEAS and molar cortisol/DHEAS-ratio of 187 remitted recurrent MDD-patients with 72 matched controls. Subsequently, patients participated in an 8-week randomized controlled cognitive therapy trial. We repeated salivary measures after 3 months and 2 years. We measured clinical symptoms during a 10-year follow-up.

RESULTS

Remitted patients showed steeper diurnal DHEAS-decline (p<.005) and a flatter diurnal profile of cortisol/DHEAS-ratio (p<.001) than controls. We found no state-effect in DHEAS or cortisol/DHEAS-ratio throughout follow-up and no association with number of previous episodes. Higher morning cortisol/DHEAS-ratio predicted shorter time till recurrence over the 10-year follow-up in interaction with the effects of cognitive therapy (p<.05). Finally, cognitive therapy did not influence DHEAS or cortisol/DHEAS-ratio.

CONCLUSIONS

Diurnal profiles of DHEAS and cortisol/DHEAS-ratio remain equally altered in between depressive episodes, and may predict future recurrence. This suggests they represent an endophenotypic vulnerability trait rather than a state-effect, which provides a new road to understand recurrent depression and its prevention.

TRIAL REGISTRATION

www.isrctn.com/ISRCTN68246470.

P-glycoprotein is fully active after multiple tryptophan substitutions

P-glycoprotein (Pgp) is an important contributor to multidrug resistance of cancer. Pgp contains eleven native tryptophans (Trps) that are highly conserved among orthologs. We replaced each Trp by a conservative substitution to determine which Trps are important for function. Individual Trp mutants W44R, W208Y, W132Y, W704Y and W851Y, situated at the membrane surface, revealed significantly reduced Pgp induced drug resistance against one or more fungicides and/or reduced mating efficiencies in Saccharomyces cerevisiae. W158F and W799F, located in the intracellular coupling helices, abolished mating but retained resistance against most drugs. In contrast, W228F and W311Y, located within the membrane, W694L, at the cytoplasmic membrane interface, and W1104Y in NBD2 retained high levels of drug resistance and mating efficiencies similar to wild-type Pgp. Those were combined into pair (W228F/W311Y and W694L/W1104Y) and quadruple (W228F/W311Y/W694L/W1104Y) mutants that were fully active in yeast, and could be purified to homogeneity. Purified pair and quad mutants exhibited drug-stimulated ATPase activity with binding affinities very similar to wild-type Pgp. The combined mutations reduced Trp fluorescence by 35%, but drug induced fluorescence quenching was unchanged from wild-type Pgp suggesting that several membrane-bound Trps are sensitive to drug binding. Overall, we conclude that Trps at the membrane surface are critical for maintaining the integrity of the drug binding sites, while Trps in the coupling helices are important for proper interdomain communication. We also demonstrate that functional single Trp mutants can be combined to form a fully active Pgp that maintains drug polyspecificity, while significantly reducing intrinsic fluorescence.

Behavioural consequences of p-glycoprotein deficiency in mice, with special focus on stress-related mechanisms

P-glycoprotein (P-gp), an efflux transporter localised in the blood-brain barrier, limits the access of multiple xenobiotics to the central nervous system. Whether it is also implemented in the transport of the endogenous glucocorticoid corticosterone is a matter of debate. The P-gp knockout mouse model [abcb1a/b (-/-)] has been shown to differ in the functioning of the hypothalamic-pituitary adrenal (HPA) axis. In the present study, we investigated the behaviour of abcb1a/b (-/-) and wild-type mice with respect to stress-related tests and the effects of corticosterone. Behavioural activities were assessed in the open field (OF) test for 4 days, and in the forced swimming test (FST) and tail suspension test (TST) under naïve and stressed conditions. The FST was also conducted after exogenous corticosterone injection (0.25 and 2.5 mg/kg). Moreover, the elevated plus maze test and the RotaRod test (RotaRod Advanced; TSE Systems, Bad Homburg, Germany) were assessed. Brain corticosterone levels were determined by an immunoassay and expression of glucocorticoid receptors by western blot analysis. Abcb1a/1b (-/-) mice showed significantly decreased brain corticosterone levels and elevated glucocorticoid receptor expression. Behavioural analysis revealed a significantly decreased activity in the OF test on the first 2 days in abcb1a/1b (-/-) mice compared to wild-type mice, although the differences disappeared under habituation. Immobility time in the FST was significantly decreased in abcb1a/1b (-/-) mice under basal and under stressed conditions, whereas immobility in the TST was significantly elevated in these mice under all conditions. Injection of exogenous corticosterone resulted in significant reductions of immobility in the FST in abcb1a/1b (-/-) mice, whereas wild-type mice did not respond to the same doses. There were no differences in the elevated plus maze test and RotaRod test. The results obtained in the present study demonstrate that a P-gp deficiency has an impact on the stress-related behaviour, possibly as a result of differences in HPA axis-feedback regulation.

Interactions between antidepressants and P-glycoprotein at the blood-brain barrier: clinical significance of in vitro and in vivo findings

The drug efflux pump P-glycoprotein (P-gp) plays an important role in the function of the blood-brain barrier by selectively extruding certain endogenous and exogenous molecules, thus limiting the ability of its substrates to reach the brain. Emerging evidence suggests that P-gp may restrict the uptake of several antidepressants into the brain, thus contributing to the poor success rate of current antidepressant therapies. Despite some inconsistency in the literature, clinical investigations of potential associations between functional single nucleotide polymorphisms in ABCB1, the gene which encodes P-gp, and antidepressant response have highlighted a potential link between P-gp function and treatment-resistant depression (TRD). Therefore, co-administration of P-gp inhibitors with antidepressants to patients who are refractory to antidepressant therapy may represent a novel therapeutic approach in the management of TRD. Furthermore, certain antidepressants inhibit P-gp in vitro, and it has been hypothesized that inhibition of P-gp by such antidepressant drugs may play a role in their therapeutic action. The present review summarizes the available in vitro, in vivo and clinical data pertaining to interactions between antidepressant drugs and P-gp, and discusses the potential relevance of these interactions in the treatment of depression.

Overexpression of P-glycoprotein, STAT3, phospho-STAT3 and KIT in spontaneous canine cutaneous mast cell tumours before and after prednisolone treatment

Prednisolone is a glucocorticoid (GC) commonly used in the treatment of canine mast cell tumours (MCTs); however, resistance to GCs develops in many MCTs following repeated treatment. P-glycoprotein (P-gp), signal transducer and activator of transcription 3 (STAT3) and KIT (CD117) are involved in GC resistance. The aim of this study was to evaluate the response to prednisolone treatment in canine cutaneous MCTs and to investigate the levels of P-gp, STAT3, phospho-STAT3 (pSTAT3) and KIT proteins in MCTs with or without prednisolone treatment. Immunohistochemistry was performed on tumour samples from 41 dogs with cutaneous MCTs. The overall objective response rate (including complete and partial responses) was 51.8% for dogs treated with prednisolone; poorly differentiated or higher stage MCTs had a lower response rate. The median time-span of tumours to reach maximal tumour regression was 14 d (range 3-77 d); 22 (81.5%) reached maximal regression at 21 d. The majority of MCTs overexpressed both P-gp and STAT3 before and after prednisolone treatment. Reduced expression of pSTAT3 and alterations in the KIT expression pattern were observed in MCTs post-treatment. Prednisolone treatment that caused a marked reduction in tumour volume was correlated with reduced pSTAT3 expression. A cytoplasmic KIT staining pattern was correlated with a lower tumour response rate to prednisolone treatment.

Aggressive interactions differentially modulate local and systemic levels of corticosterone and DHEA in a wild songbird

During the nonbreeding season, when gonadal androgen synthesis is basal, recent evidence suggests that neurosteroids regulate the aggression of male song sparrows. In particular, dehydroepiandrosterone (DHEA) is rapidly converted in the brain to androgens in response to aggressive interactions. In other species, aggressive encounters increase systemic glucocorticoid levels. However, the relationship between aggression and local steroid levels is not well understood. Here, during the breeding and nonbreeding seasons, we tested the effects of a simulated territorial intrusion (STI) on DHEA and corticosterone levels in the brachial and jugular plasma. Jugular plasma is enriched with neurosteroids and provides an indirect index of brain steroid levels. Further, during the nonbreeding season, we directly measured steroid levels in the brain and peripheral tissues. Both breeding and nonbreeding males displayed robust aggressive responses to STI. During the breeding season, STI increased brachial and jugular corticosterone levels and jugular DHEA levels. During the nonbreeding season, STI did not affect plasma corticosterone levels, but increased jugular DHEA levels. During the nonbreeding season, STI did not affect brain levels of corticosterone or DHEA. However, STI did increase corticosterone and DHEA concentrations in the liver and corticosterone concentrations in the pectoral muscle. These data suggest that 1) aggressive social interactions affect neurosteroid levels in both seasons and 2) local steroid synthesis in peripheral tissues may mobilize energy reserves to fuel aggression in the nonbreeding season. Local steroid synthesis in brain, liver or muscle may serve to avoid the costs of systemic increases in corticosterone and testosterone.

A gene optimization strategy that enhances production of fully functional P-glycoprotein in Pichia pastoris

BACKGROUND

Structural and biochemical studies of mammalian membrane proteins remain hampered by inefficient production of pure protein. We explored codon optimization based on highly expressed Pichia pastoris genes to enhance co-translational folding and production of P-glycoprotein (Pgp), an ATP-dependent drug efflux pump involved in multidrug resistance of cancers.

METHODOLOGY/PRINCIPAL FINDINGS

Codon-optimized "Opti-Pgp" and wild-type Pgp, identical in primary protein sequence, were rigorously analyzed for differences in function or solution structure. Yeast expression levels and yield of purified protein from P. pastoris (∼130 mg per kg cells) were about three-fold higher for Opti-Pgp than for wild-type protein. Opti-Pgp conveyed full in vivo drug resistance against multiple anticancer and fungicidal drugs. ATP hydrolysis by purified Opti-Pgp was strongly stimulated ∼15-fold by verapamil and inhibited by cyclosporine A with binding constants of 4.2±2.2 µM and 1.1±0.26 µM, indistinguishable from wild-type Pgp. Maximum turnover number was 2.1±0.28 µmol/min/mg and was enhanced by 1.2-fold over wild-type Pgp, likely due to higher purity of Opti-Pgp preparations. Analysis of purified wild-type and Opti-Pgp by CD, DSC and limited proteolysis suggested similar secondary and ternary structure. Addition of lipid increased the thermal stability from T(m) ∼40 °C to 49 °C, and the total unfolding enthalpy. The increase in folded state may account for the increase in drug-stimulated ATPase activity seen in presence of lipids.

CONCLUSION

The significantly higher yields of protein in the native folded state, higher purity and improved function establish the value of our gene optimization approach, and provide a basis to improve production of other membrane proteins.

Anti-inflammatory glucocorticoid drugs: reflections after 60 years

This review considers the problem of the serious concomitant side effects of powerful anti-inflammatory drugs modelled upon the principal human glucocorticoid hormone, cortisol. The very nature of the original bio-assays to validate their cortisol-like hormonal and anti-inflammatory activities ensured that pleiotropic toxins were selected for clinical studies. Other complicating factors have been (1) considerable reliance on bio-assays conducted in laboratory animals that primarily secrete corticosterone, not cortisol, as their principal anti-inflammatory adrenal hormone; (2) some differences in the binding of xenobiotic cortisol analogues (vis á vis cortisol) to transport proteins, detoxifying enzymes and even some intra-cellular receptors; (3) the "rogue" properties of these hormonal xenobiotics, acting independently of--but still able to suppress--hormonal mechanisms regulating endogenous cortisol; and (4) problems of intrinsic/acquired "steroid resistance", diminishing their clinical efficacy, but not necessarily all their toxicities. The rather gloomy conclusion is that devising new drugs to reproduce the effect of multi-potent hormones may be a recipe for disaster, in contexts other than simply remedying an endocrine deficiency. Promising new developments include "designed" combination therapies that allow some reduction in total steroid doses (and hopefully their side effects); sharpening strategies to limit the actual duration of steroid administration; and resurgent interest in searching for more selective analogues (both steroidal and non-steroid) with less harmful side effects. Some oversights and neglected areas of research are also considered. Overall, it now seems timely to engage in some drastic rethinking about (retaining?) these "licensed toxins" as fundamental therapies for chronic inflammation.

Determinants of Tc-99m sestamibi SPECT scan sensitivity in primary hyperparathyroidism

BACKGROUND

The aim of this study was to evaluate the influence of patient and adenoma characteristics on (99m)Tc-methoxy isobutyl isonitrile (MIBI) scan performance in individuals diagnosed with primary hyperparathyroidism (PHP).

METHODS

Records of patients undergoing parathyroidectomy for PHP over 6 years at a single center were reviewed.

RESULTS

The overall true-positive (TP) rate for (99m)Tc-MIBI scans was 56%. Adenomas sized 1.9 to 3.5 cm were more likely to have TP scans than 0.3-cm to 1.8-cm adenomas (74% vs 40%, P < .001). Preoperative ionized calcium levels between 1.49 and 1.72 mmol/L were more likely to have TPs than levels between 1.27 and 1.48 mmol/L (65% vs 47%, P < .05). No single class of medication was shown to significantly effect TP rates. A decrease in TP rate was observed for larger adenomas in patients on >or=1 medication (74% vs 65%, P = .05).

CONCLUSIONS

In PHP, (99m)Tc-MIBI scan positivity is most related to adenoma size and preoperative ionized calcium level.

Cytokines and glucocorticoid receptor signaling. Relevance to major depression

Data suggest that the activation of immune responses and the release of inflammatory cytokines may play a role in the pathophysiology of major depression. One mechanism by which cytokines may contribute to depression is through their effects on the glucocorticoid receptor (GR). Altered GR function in depression has been demonstrated by neuroendocrine challenge tests that reliably reveal reduced GR sensitivity as manifested by nonsuppression of cortisol following dexamethasone administration in vivo and lack of immune suppression following administration of glucocorticoids in vitro. Relevant to the GR, cytokines have been shown to decrease GR expression, block translocation of the GR from cytoplasm to nucleus, and disrupt GR-DNA binding through nuclear protein-protein interactions. In addition, cytokines have been shown to increase the expression of the relatively inert GR beta isoform. Specific cytokine signaling molecules that have been shown to be involved in the disruption of GR activity include p38 mitogen-activated protein kinase, which is associated with reduced GR translocation, and signal transducer and activator of transcription (STAT)5, which binds to GR in the nucleus. Nuclear factor-kappaB (NF-kappaB) also has been shown to lead to GR suppression through mutually inhibitory GR-NF-kappaB nuclear interactions. Interestingly, several antidepressants have been shown to enhance GR function, as has activation of protein kinase A (PKA). Antidepressants and PKA activation have also been found to inhibit inflammatory cytokines and their signaling pathways, suggesting that drugs that target both inflammatory responses and the GR may have special efficacy in the treatment of depression.

Risk factors for development of depression and psychosis. Glucocorticoid receptors and pituitary implications for treatment with antidepressant and glucocorticoids

Increased levels of glucocorticoid hormones-the main product of the hypothalamic-pituitary-adrenal (HPA) axis-have been considered to be "depressogenic," but this notion has largely derived from studies in patients with endocrine conditions, such as Cushing's syndrome or exogenous treatment with synthetic glucocorticoids. In these conditions, it is likely that the full impact of the high glucocorticoid levels is felt on the brain, through over-stimulation of the glucocorticoid receptors (GRs); indeed, normalizing these high levels leads to an improvement of mood in these patients. However, a completely different mechanism may be operating in major depression, where the increased levels of glucocorticoid hormones are conceptualized as driven by an impairment in GR function (glucocorticoid resistance), and therefore as a "compensatory" mechanism. Moreover, clinical and experimental studies have shown that antidepressants increase GR function, thus leading to resolution of glucocorticoid resistance. Interestingly, a number of studies have also demonstrated that manipulating GR function with both agonists and antagonists has an antidepressant effect, and indeed that other drugs targeting the HPA axis and cortisol secretion-even drugs with opposite effects on the HPA axis-have antidepressant effects. These studies do not support the notion that "high levels of glucocorticoids" always have a depressogenic effect, nor that decreasing the effects of these hormones always has an antidepressant effects.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Improved stress response in bipolar affective disorder with adjunctive spironolactone (mineralocorticoid receptor antagonist): case series

The psychopathologies underlying affective disorders are thought to involve persistent changes in the expression and function of both mineralocorticoid receptors and glucocorticoid receptors in the hippocampus. In addition, exposure to stressful stimuli can precipitate episodes in vulnerable individuals. The aim of this study is to determine if spironolactone as an adjunctive therapy is effective in improving residual symptoms in bipolar disorder. Four cases of euthymic bipolar disorder (BD) patients were treated with spironolactone as an adjunctive therapy in a private treatment sector. All patients met the DSM-IV diagnosis criteria for bipolar disorder. Clinical response was assessed retrospectively using the Clinical Global Impression Scale for Improvement. Spironolactone was effective in all patients. The four cases illustrate a clinical response to residual symptoms and improvement in stress response after use of spironolactone as an adjunctive therapy in BD. This pilot case series suggests reducing in residual symptoms, with spironolactone as an adjunctive therapy in these DSM-IV BD patients. Mineralocorticoid receptors antagonists' role in reducing stress-induced symptoms deserves further investigation through placebo-controlled trials.

Glucocorticoid dysregulations and their clinical correlates. From receptors to therapeutics

Clinicians have long known that a substantial proportion of patients treated with high-dose glucocorticoids experience a variety of serious side effects, including metabolic syndrome, bone loss, and mood shifts, such as depressive symptomatology, manic or hypomanic symptoms, and even suicide. The reason for individual variability in expression or severity of these side effects is not clear. However, recent emerging literature is beginning to shed light on possible mechanisms of these effects. As an introduction to this volume, this chapter will review the basic biology of glucocorticoid release and molecular mechanisms of glucocorticoid receptor function, and will discuss how dysregulation of glucocorticoid action at all levels could contribute to such side effects. At the molecular level, glucocorticoid receptor polymorphisms may be associated either with receptor hypofunction or hyperfunction and could thus contribute to differential individual sensitivity to the effects of glucocorticoid treatment. Numerous factors regulate hypothalamic-pituitary-adrenal (HPA) axis responsiveness, which could also contribute to individual differences in glucocorticoid side effects. One of these is sex hormone status and the influence of estrogen and progesterone on HPA axis function and mood. Another is immune system activity, in which immune molecules, such as interleukins and cytokines, activate the HPA axis and alter brain function, including memory, cognition, and mood. The effects of cytokines in inducing sickness behaviors, which overlap with depressive symptomatology, could also contribute to individual differences in such symptomatology. Taken together, this knowledge will have important relevance for identifying at-risk patients to avoid or minimize such side effects when they are treated with glucocorticoids. A framework for assessment of patients is proposed that incorporates functional, physiological, and molecular biomarkers to identify subgroups of patients at risk for depressive symptomatology associated with glucocorticoid treatment, and for prevention of side effects, which in many cases can be life-threatening.

Glucocorticoid replacement therapy and pharmacogenetics in Addison's disease: effects on bone

Context Patients with primary adrenal insufficiency (Addison's disease) receive more glucococorticoids than the normal endogenous production, raising concern about adverse effects on bone.

OBJECTIVE

To determine i) the effects of glucocorticoid replacement therapy on bone, and ii) the impact of glucocorticoid pharmacogenetics.

DESIGN, SETTING AND PARTICIPANTS

A cross-sectional study of two large Addison's cohorts from Norway (n=187) and from UK and New Zealand (n=105).

MAIN OUTCOME MEASURES

Bone mineral density (BMD) was measured; the Z-scores represent comparison with a reference population. Blood samples from 187 Norwegian patients were analysed for bone markers and common polymorphisms in genes that have been associated with glucocorticoid sensitivity.

RESULTS

Femoral neck BMD Z-scores were significantly reduced in the patients (Norway: mean -0.28 (95% confidence intervals (CI) -0.42, -0.16); UK and New Zealand: -0.21 (95% CI -0.36, -0.06)). Lumbar spine Z-scores were reduced (Norway: -0.17 (-0.36, +0.01); UK and New Zealand: -0.57 (-0.78, -0.37)), and significantly lower in males compared with females (P=0.02). The common P-glycoprotein (ABCB1) polymorphism C3435T was significantly associated with total BMD (CC and CT>TT P=0.015), with a similar trend at the hip and spine.

CONCLUSIONS

BMD at the femoral neck and lumbar spine is reduced in Addison's disease, indicating undesirable effects of the replacement therapy. The findings lend support to the recommendations that 15-25 mg hydrocortisone daily is more appropriate than the higher conventional doses. A common polymorphism in the efflux transporter P-glycoprotein is associated with reduced bone mass and might confer susceptibility to glucocorticoid induced osteoporosis.

Corticosterone and dehydroepiandrosterone in songbird plasma and brain: effects of season and acute stress

Prolonged increases in plasma glucocorticoids can exacerbate neurodegeneration. In rats, these neurodegenerative effects can be reduced by dehydroepiandrosterone (DHEA), an androgen precursor with anti-glucocorticoid actions. In song sparrows, season and acute restraint stress affect circulating levels of corticosterone and DHEA, and the effects of stress differ in plasma collected from the brachial and jugular veins. Jugular plasma is an indirect index of the neural steroidal milieu. Here, we directly measured corticosterone and DHEA in several brain regions and jugular plasma, and examined the effects of season and acute restraint stress (30 min) (n = 571 samples). Corticosterone levels were up to 10x lower in brain than in jugular plasma. In contrast, DHEA levels were up to 5x higher in brain than in jugular plasma and were highest in the hippocampus. Corticosterone and DHEA concentrations were strongly seasonally regulated in plasma but, surprisingly, not seasonally regulated in brain. Acute stress increased corticosterone levels in plasma and brain, except during the molt, when stress unexpectedly decreased corticosterone levels in the hippocampus. Acute stress increased DHEA levels in plasma during the molt but had no effects on DHEA levels in brain. This is the first study to measure (i) corticosterone or DHEA levels in the brain of adult songbirds and (ii) seasonal changes in corticosterone or DHEA levels in the brain of any species. These results highlight several critical differences between systemic and local steroid concentrations and the difficulty of using circulating steroid levels to infer local steroid levels within the brain.

Mechanisms regulating the susceptibility of hematopoietic malignancies to glucocorticoid-induced apoptosis

Glucocorticoids (GCs) are commonly used in the treatment of hematopoietic malignancies owing to their ability to induce apoptosis of these cancerous cells. Whereas some types of lymphoma and leukemia respond well to this drug, others are resistant. Also, GC-resistance gradually develops upon repeated treatments ultimately leading to refractory relapsed disease. Understanding the mechanisms regulating GC-induced apoptosis is therefore uttermost important for designing novel treatment strategies that overcome GC-resistance. This review discusses updated data describing the complex regulation of the cell's susceptibility to apoptosis triggered by GCs. We address both the genomic and nongenomic effects involved in promoting the apoptotic signals as well as the resistance mechanisms opposing these signals. Eventually we address potential strategies of clinical relevance that sensitize GC-resistant lymphoma and leukemia cells to this drug. The major target is the nongenomic signal transduction machinery where the interplay between protein kinases determines the cell fate. Shifting the balance of the kinome towards a state where Glycogen synthase kinase 3alpha (GSK3alpha) is kept active, favors an apoptotic response. Accumulating data show that it is possible to therapeutically modulate GC-resistance in patients, thereby improving the response to GC therapy.

A revised role for P-glycoprotein in the brain distribution of dexamethasone, cortisol, and corticosterone in wild-type and ABCB1A/B-deficient mice

The ABCB1-type multidrug resistance efflux transporter P-glycoprotein (P-gp) has been hypothesized to regulate hypothalamic-pituitary-adrenal axis activity by limiting the access of glucocorticoids to the brain. In vivo systemic administration studies using P-gp-deficient mice have shown increased glucocorticoid entry to the brain compared with wild-type controls. However, these studies did not control for the presence of radiolabeled drug in the capillaries, verify an intact blood-brain barrier, or confirm stability of the glucocorticoids used. In the present study, an in situ brain perfusion method, coupled with capillary depletion and HPLC analyses, was used to quantify brain uptake of [3H]dexa-methasone, [3H]cortisol, and [3H]corticosterone in P-gp-deficient and control mice. A vascular marker was included in these experiments. The results show that brain uptake of [3H]dexamethasone was increased in the frontal cortex, hippocampus, hypothalamus, and cerebellum of P-gp-deficient mice compared with wild-type controls. Brain uptake of [3H]cortisol was increased in the hypothalamus of P-gp-deficient mice compared with wild-type controls, but no differences were detected in other regions. Brain uptake of [3H]corticosterone was not increased in P-gp-deficient mice compared with wild-type controls in any brain areas. After our systemic administration of the same radiolabeled glucocorticoids, HPLC analysis of plasma samples identified additional radiolabeled components, likely to be metabolites. This could explain previous findings from systemic administration studies, showing an effect of P-gp not only for dexamethasone and cortisol, but also for corticosterone. This in situ study highlights the different affinities of dexamethasone, cortisol, and corticosterone for P-gp, and suggests that the entry of the endogenous glucocorticoids into the mouse brain is not tightly regulated by P-gp. Therefore, our current understanding of the role of P-gp in hypothalamic-pituitary-adrenal regulation in mice requires revision.