Effects of dissociated glucocorticoids on OPG and RANKL in osteoblastic cells

A structural explanation of the effects of dissociated glucocorticoids on glucocorticoid receptor transactivation

There is a therapeutic need for glucocorticoid receptor (GR) ligands that distinguish between the transrepression and transactivation activity of the GR, the later thought to be responsible for side effects. These ligands are known as "dissociated glucocorticoids" (dGCs). The first published dGCs, RU24782 (9α-fluoro-11β-hydroxy-16α-methylpregna-21-thiomethyl-1,4-diene-3,20-dione) and RU24858 (9α-fluoro-11β-hydroxy-16α-methylpregna-21-cyanide-1,4-diene-3,20-dione), do not have the 17α-hydroxyl group that characterizes dexamethasone (Dex; 9α-fluoro-11β,17α,21-trihydroxy-16α-methylpregna-1,4-diene-3,20-dione), and they differ from one another by having C21-thiomethyl and C21-cyanide moieties, respectively. Our aim was therefore to establish the structural basis of their activity. Both RU24782 and RU24858 induced a transactivation activity highly dependent on the GR expression level but always lower than dexamethasone. They also display less ability than dexamethasone to trigger steroid receptor coactivator 1 (SRC-1) recruitment and histone H3 acetylation. Docking studies, validated by mutagenesis experiments, revealed that dGCs are not anchored by Gln642, in contrast to Dex, which is hydrogen bonded to this residue via its 17α-hydroxyl group. This contact is essential for SRC-1 recruitment and subsequent dexamethasone-induced GR transactivation, but not transrepression. The ability of dGCs to make contacts with Ile747, for both RU24858 and RU24782 and with Asn564 for RU24858 are not strong enough to maintain GR in a conformation able to efficiently recruit SRC-1, unless SRC-1 is overexpressed. Overall, our findings provide some structural guidelines for the synthesis of potential new dissociated glucocorticoids with a better therapeutic ratio.

Effects of proteasome inhibitors on bone cancer

Bone metastasis is a frequent complication of cancer, occurring in up to 70% of patients with advanced breast or prostate cancer, while bone disease is also the characteristic clinical feature of multiple myeloma. Skeletal-related events can be devastating, with major effect on the quality of life and survival. Bisphosphonates are the mainstay of therapeutic management of bone disease of solid tumors and myeloma, and denosumab has recently been approved for patients with bone metastases. Both act through inhibition of the osteoclast activity but do not restore bone formation. Proteasome inhibition has direct bone anabolic effects. Proteasome inhibitors have been used in the management of patients with multiple myeloma and mantle-cell lymphoma during the last decade. In multiple myeloma, bortezomib, the first-in-class proteasome inhibitor, has shown both in vitro and in vivo regulation of bone remodeling by inhibiting osteoclast function and promoting osteoblast activity. Bortezomib also reduces bone resorption but more importantly increases bone formation and bone mineral density, at least, in subsets of myeloma patients. Thus, bortezomib is recommended for myeloma patients with extended bone disease in combination with bisphosphonates. This review focuses on the effects of the proteasome system on bone metabolism and the implications into the better management of patients with cancer and bone disease.

Curculigoside promotes osteogenic differentiation of bone marrow stromal cells from ovariectomized rats

OBJECTIVES

Curculigoside, a natural compound isolated from the medicinal plant Curculigo orchioides has been reported to prevent bone loss in ovariectomized rats. However, the underlying molecular mechanisms are largely unknown. This study investigated the effects of curculigoside on proliferation and osteogenic differentiation of bone marrow stromal cells (BMSCs).

METHODS

The toxicity, proliferation and osteogenic differentiation of BMSCs cultured with various concentrations (0 as control, 10, 100 and 500 µm) of curculigoside were measured by viability assay, MTT analysis, alkaline phosphatase (ALP) activity assay, alizarin red staining and mineralization assay, real-time PCR analysis on osteogenic genes including ALP, type I collagen (Col I), osteocalcin (OCN) and osteoprotegerin (OPG), runt-related transcription factor 2 (Runx2), as well as OPG enzyme-linked immunosorbent assay.

KEY FINDINGS

No significant cytotoxicity was observed for BMSCs after supplementation with curculigoside. The proliferation of BMSCs was enhanced after administration of curculigoside, especially 100 µm curculigoside. Moreover, the osteogenic gene expression was significantly enhanced with 100 µm curculigoside treatment. Importantly, curculigoside significantly increased OPG secretion.

CONCLUSIONS

The data indicate that curculigoside could promote BMSC proliferation and induce osteogenic differentiation of BMSCs. The most profound response was observed with 100 µm curculigoside. These findings may be valuable for understanding the mechanism of the effect of curculigoside on bone, especially in relation to osteoporosis.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Rib fractures and death from deletion of osteoblast βcatenin in adult mice is rescued by corticosteroids

Ribs are primarily made of cortical bone and are necessary for chest expansion and ventilation. Rib fractures represent the most common type of non-traumatic fractures in the elderly yet few studies have focused on the biology of rib fragility. Here, we show that deletion of βcatenin in Col1a2 expressing osteoblasts of adult mice leads to aggressive osteoclastogenesis with increased serum levels of the osteoclastogenic cytokine RANKL, extensive rib resorption, multiple spontaneous rib fractures and chest wall deformities. Within days of osteoblast specific βcatenin deletion, animals die from respiratory failure with a vanishing rib cage that is unable to sustain ventilation. Increased bone resorption is also observed in the vertebrae and femur. Treatment with the bisphosphonate pamidronate delayed but did not prevent death or associated rib fractures. In contrast, administration of the glucocorticoid dexamethasone decreased serum RANKL and slowed osteoclastogenesis. Dexamethasone preserved rib structure, prevented respiratory compromise and strikingly increased survival. Our findings provide a novel model of accelerated osteoclastogenesis, where deletion of osteoblast βcatenin in adults leads to rapid development of destructive rib fractures. We demonstrate the role of βcatenin dependent mechanisms in rib fractures and suggest that glucocorticoids, by suppressing RANKL, may have a role in treating bone loss due to aggressive osteoclastogenesis.

Noncanonical mechanisms to regulate nuclear receptor signaling

Nuclear receptor (NR)-targeted therapies comprise a large class of clinically employed drugs. A number of drugs currently being used against this protein class were designed as structural analogs of the endogenous ligand of these receptors. In recent years, there has been significant interest in developing newer strategies to target NRs, especially those that rely on mechanistic pathways of NR function. Prominent among these are noncanonical means of targeting NRs, which include selective NR modulation, NR coactivator interaction inhibition, inhibition of NR DNA binding, modulation of NR cellular localization, modulation of NR ligand biosynthesis and downregulation of NR levels in target tissues. This article reviews each of these promising emerging strategies for NR drug development and highlights some of most significant successes achieved in using them.

Selective glucocorticoid receptor modulation maintains bone mineral density in mice

Glucocorticoids (GCs) are potent anti-inflammatory drugs, but their use is limited by their adverse effects on the skeleton. Compound A (CpdA) is a novel GC receptor modulator with the potential for an improved risk/benefit profile. We tested the effects of CpdA on bone in a mouse model of GC-induced bone loss. Bone loss was induced in FVB/N mice by implanting slow-release pellets containing either vehicle, prednisolone (PRED) (3.5 mg), or CpdA (3.5 mg). After 4 weeks, mice were killed to examine the effects on the skeleton using quantitative computed tomography, bone histomorphometry, serum markers of bone turnover, and gene expression analysis. To assess the underlying mechanisms, in vitro studies were performed with human bone marrow stromal cells (BMSCs) and murine osteocyte-like cells (MLO-Y4 cells). PRED reduced the total and trabecular bone density in the femur by 9% and 24% and in the spine by 11% and 20%, respectively, whereas CpdA did not influence these parameters. Histomorphometry confirmed these results and further showed that the mineral apposition rate was decreased by PRED whereas the number of osteoclasts was increased. Decreased bone formation was paralleled by a decline in serum procollagen type 1 N-terminal peptide (P1NP), reduced skeletal expression of osteoblast markers, and increased serum levels of the osteoblast inhibitor dickkopf-1 (DKK-1). In addition, serum CTX-1 and the skeletal receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) ratio were increased by PRED. None of these effects were observed with CpdA. Consistent with the in vivo data, CpdA did not increase the RANKL/OPG ratio in MLO-Y4 cells or the expression of DKK-1 in bone tissue, BMSCs, and osteocytes. Finally, CpdA also failed to transactivate DKK-1 expression in bone tissue, BMSCs, and osteocytes. This study underlines the bone-sparing potential of CpdA and suggests that by preventing increases in the RANKL/OPG ratio or DKK-1 in osteoblast lineage cells, GC-induced bone loss may be ameliorated.

Circulating sclerostin levels are decreased in patients with endogenous hypercortisolism and increase after treatment

CONTEXT

Increased bone fragility is a frequent complication of hypercortisolism due predominantly to suppression of bone formation. Sclerostin is an osteocyte-produced negative regulator of bone formation, which is up-regulated by glucocorticoids in mice.

OBJECTIVE

Our objective was to assess the effect of endogenous hypercortisolism on circulating sclerostin and bone turnover in humans.

DESIGN

We measured sclerostin, β-C-terminal telopeptide, amino-terminal propeptide of type 1 procollagen, and fibroblast growth factor 23 in blood samples of 21 patients with endogenous hypercortisolism and 21 age- and gender-matched controls. In 12 patients, measurements were repeated at various time intervals after successful surgical treatment (transsphenoidal surgery or adrenalectomy).

RESULTS

Plasma sclerostin levels were significantly decreased in patients compared with controls (112±49 vs. 207±48 pg/ml, P<0.001). In the 12 patients who were evaluated after surgical treatment, sclerostin levels increased from 121.4±46.5 to 175.8±78.5 pg/ml (P=0.003). These changes in plasma sclerostin levels were accompanied by significant increases in levels of fibroblast growth factor 23 (from 44.2±12.2 to 84.0±58.8 pg/ml, P=0.017) and of the bone turnover markers amino-terminal propeptide of type 1 procollagen (from 31.7±18.2 to 94.2±92.2 ng/ml, P=0.037) and β-C-terminal telopeptide (from 134.2±44 to 409.2±285 pg/ml, P=0.005).

CONCLUSIONS

Contrary to the findings in mice, circulating sclerostin is decreased in patients with chronic endogenous hypercortisolism and increases after treatment. These findings suggest that in humans, chronic exposure to glucocorticoids affects the number or function of osteocytes rather than the production of sclerostin.

Changes of serum soluble receptor activator for nuclear factor-κB ligand after glucocorticoid therapy reflect regulation of its expression by osteoblasts

CONTEXT

Osteoporosis is a serious complication of systemic glucocorticoid therapy. The role of serum soluble receptor activator for nuclear factor-κB ligand (RANKL) in glucocorticoid-induced osteoporosis remains unclear.

OBJECTIVE

The objective of the study was to clarify the influence of serum soluble RANKL on the osteoprotegerin (OPG)/RANKL/receptor activator for nuclear factor-κB system in patients with systemic autoimmune diseases receiving glucocorticoid therapy.

PATIENTS AND METHODS

Sixty patients (40 women) with systemic autoimmune diseases who received initial glucocorticoid therapy with prednisolone (30-60 mg/d) plus bisphosphonate therapy were prospectively enrolled. Serum soluble RANKL and OPG levels were measured at 0, 1, 2, 3, and 4 wk after starting glucocorticoid therapy. The effects of dexamethasone on production of RANKL and OPG mRNA and protein by cultured normal human osteoblasts were evaluated by RT-PCR and ELISA, respectively.

RESULTS

The mean serum soluble RANKL level of the patients was unchanged by glucocorticoid therapy. Because the distribution of serum soluble RANKL was bimodal, the patients were stratified into two groups. Serum soluble RANKL decreased significantly in the higher soluble RANKL group (≥0.16 pmol/liter), whereas it increased significantly in the lower soluble RANKL group. The mean serum OPG level of the patients decreased significantly. Bone mineral density increased in the higher soluble RANKL group after starting glucocorticoid therapy, whereas it decreased in the lower soluble RANKL group. In cultures of unstimulated human osteoblasts, RANKL mRNA expression was increased and OPG mRNA was decreased by dexamethasone. Up-regulation of RANKL and OPG mRNA by IL-6 was suppressed by dexamethasone.

CONCLUSION

Serum soluble RANKL might be a useful marker of bone remodeling in patients with systemic autoimmune diseases receiving glucocorticoid therapy.

Poncirin prevents bone loss in glucocorticoid-induced osteoporosis in vivo and in vitro

Poncirin, a flavonoid isolated from the fruit of Poncirus trifoliata, possesses anti-bacterial and anti-inflammatory activities. However, the action of poncirin in bone biology is unclear. In this study, the in vivo and in vitro effects of poncirin in a glucocorticoid-induced osteoporosis (GIO) mouse model were investigated. Seven-month-old male mice were assigned to the following five groups: (1) sham-implantation (sham), (2) prednisolone 2.1 mg/kg/day (GC), (3) GC treated with 10 mg/kg/day of genistein, (4) GC treated with 3 mg/kg/day of poncirin, (5) and GC treated with 10 mg/kg/day of strontium (GC + SrCl(2)). After 8 weeks, bone loss was measured by microcomputed tomography. Osteocalcin (OC) and C-terminal telopeptides of type I collagen (CTX) were evaluated in sera. Runx2 protein, OC and osteoprotegerin (OPG) mRNA expression, alkaline phosphatase (ALP) activity, and mineral nodule assay were performed in C3H10T1/2 or primary bone marrow stromal cells. Poncirin significantly increased the bone mineral density and improved the microarchitecture. Poncirin increased serum OC, Runx2 protein production, expression of OC and OPG mRNA, ALP activity, and mineral nodule formation; and decreased serum CTX. These effects were more prominent in the poncirin group compared to the other positive control groups (genistein and strontium). The poncirin-mediated restoration of biochemical bone markers, increased bone mineral density, and improved trabecular microarchitecture likely reflect increased bone formation and decreased bone resorption in GIO mice.

Anti-inflammatory effects of selective glucocorticoid receptor modulators are partially dependent on up-regulation of dual specificity phosphatase 1

BACKGROUND AND PURPOSE

It is thought that the anti-inflammatory effects of glucocorticoids (GCs) are largely due to GC receptor (GR)-mediated transrepression of NF-κB and other transcription factors, whereas side effects are caused by activation of gene expression (transactivation). Selective GR modulators (SGRMs) that preferentially promote transrepression should retain anti-inflammatory properties whilst causing fewer side effects. Contradicting this model, we found that anti-inflammatory effects of the classical GC dexamethasone were partly dependent on transactivation of the dual specificity phosphatase 1 (DUSP1) gene. We wished to determine whether anti-inflammatory effects of SGRMs are also mediated by DUSP1.

EXPERIMENTAL APPROACH

Dissociated properties of two SGRMs were confirmed using GR- and NF-κB-dependent reporters, and capacity to activate GC-responsive elements of the DUSP1 gene was tested. Effects of SGRMs on the expression of DUSP1 and pro-inflammatory gene products were assessed in various cell lines and in primary murine Dusp1(+/+) and Dusp1(-/-) macrophages.

KEY RESULTS

The SGRMs were able to up-regulate DUSP1 in several cell types, and this response correlated with the ability of the compounds to suppress COX-2 expression. Several anti-inflammatory effects of SGRMs were ablated or significantly impaired in Dusp1(-/-) macrophages.

CONCLUSIONS AND IMPLICATIONS

Like dexamethasone, SGRMs appear to exert anti-inflammatory effects partly via the up-regulation of DUSP1. This finding has implications for how potentially therapeutic novel GR ligands are identified and assessed.

Selective glucocorticoid receptor agonists for the treatment of inflammatory bowel disease: studies in mice with acute trinitrobenzene sulfonic acid colitis

Despite being a mainstay of inflammatory bowel disease (IBD) therapy, glucocorticoids (GCs) still carry significant risks with respect to unwanted side effects. Alternative drugs with a more favorable risk/benefit ratio than common GCs are thus highly desirable for the management of IBD. New and supposedly selective glucocorticoid receptor (GR) agonists (SEGRAs), with dissociated properties, have been described as promising candidates for circumventing therapeutic problems while still displaying full beneficial anti-inflammatory potency. Here, we report on compound A [CpdA; (2-((4-acetophenyl)-2-chloro-N-methyl)ethylammonium-chloride)] and N-(4-methyl-1-oxo-1H-2,3-benzoxazine-6-yl)-4-(2,3-dihydrobenzofuran-7-yl)-2-hydroxy-2-(trifluoromethyl)-4-methylpentanamide (ZK216348), two GR agonists for the treatment of experimental colitis. Their therapeutic and anti-inflammatory effects were tested in the acute trinitrobenzene sulfonic acid-mediated colitis model in mice against dexamethasone (Dex). In addition to their influence on immunological pathways, a set of possible side effects, including impact on glucose homeostasis, steroid resistance, and induction of apoptosis, was surveyed. Our results showed that, comparable with Dex, treatment with CpdA and ZK216348 reduced the severity of wasting disease, macroscopic and microscopic damage, and colonic inflammation. However, both SEGRAs exhibited no GC-associated diabetogenic effects, hypothalamic pituitary adrenal axis suppression, or development of glucocorticoid resistance. In addition, CpdA and ZK216348 showed fewer transactivating properties and successfully dampened T helper 1 immune response. Unlike ZK216348, the therapeutic benefit of CpdA was lost at higher doses because of toxic apoptotic effects. In conclusion, both SEGRAs acted as potent anti-inflammatory agents with a significantly improved profile compared with classic GCs. Although CpdA revealed a narrow therapeutic window, both GR agonists might be seen as a starting point for a future IBD treatment option.

Simultaneous administration of fluoride and selenite regulates proliferation and apoptosis in murine osteoblast-like MC3T3-E1 cells by altering osteoprotegerin

The receptor activator nuclear factor kappa-B ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG), are important for maintaining the balance between bone formation and resorption. However, the regulation of microelements on these factors remains unclear. In this study, we used murine osteoblast-like MC3T3-E1 cells to examine the impact of sodium fluoride (NaF) and/or sodium selenite (Na2SeO3) on the OPG/RANKL system. MC3T3-E1 cells were treated with OPG or RANKL siRNA (or left untreated), and subsequently divided into a control group and five experimental groups, which were exposed to different concentrations of NaF and/or Na2SeO3, and subsequently analysed at 24 h. In particular, we examined cell viability, OPG and RANKL mRNA and protein expression, caspase-3 activity, and the cell cycle of the various cell groups. In summary, our findings suggest that the administration of NaF and/or Na2SeO3 affects the expression of OPG in osteoblast-like MC3T3-E1 cells, thereby contributing to the proliferation and apoptosis induced by the OPG.

Role of RANKL-RANK/osteoprotegerin molecular complex in bone remodeling and its immunopathologic implications

Bone remodeling is a cyclic and continuous physiological process, which ensures the conservation and renewal of the bone matrix. Osteosynthesis of the bone matrix is achieved by osteoblasts and coordinated within this complex machinery of bone remodeling with resorption of extracellular bone matrix performed by osteoclasts. The mismatch between the activities of osteoblasts and osteoclasts has immunopathologic implications associated with either a decrease or increase of bone mass mineral density. The balance of the trimolecular control factor complex composed of osteoprotegerin (OPG), RANKL (osteoprotegerin ligand) and RANK maintains physiologic bone remodeling. This trimolecular complex functions as receptors and ligands and belongs to the superfamily of tumor necrosis factor (TNF). This mini review highlights the complex interplay of the RANKL-RANK/OPG axis and their immunopathologic implications in clinical medicine.

Quantitative ultrasound measurements in premature infants at 1 year of age: the effects of antenatal administered corticosteroids

The aim of this study was to evaluate the effects of antenatally administered glucocorticoids on bone status of preterm infants at 1 year corrected age. The study population consisted of 32 preterm infants with a gestational age of 24-34 weeks. The infants were divided into two groups according to antenatal exposure to corticosteroids. Quantitative ultrasound (QUS) assessment of bone was performed in the study infants at the corrected age of 1 year. Blood levels of carboxy-terminal propeptide of type I procollagen (PICP) and carboxy-terminal telopeptide of type I collagen (ICTP) were measured at birth and at 1 year corrected age. Levels of PICP and ICTP were significantly lower at birth in corticosteroid-exposed neonates (P < 0.05). At corrected age of 12 months ICTP levels remained significantly lower in corticosteroid-exposed infants, but we found no significant difference in levels of the bone-formation marker PICP between corticosteroid-exposed and nonexposed infants. In the majority of participant preterm infants bone speed of sound (SOS) was within age-adjusted normal values of full-term infants. There was no significant difference in bone SOS between exposed and nonexposed infants at corrected age of 12 months. There was no correlation between SOS and levels of bone markers. The results of our study indicate that, despite the suppression of fetal bone turnover at birth in corticosteroid-exposed infants, antenatal glucocorticoid treatment seems to have no long-term impact on bone status of preterm infants assessed by QUS complementary to measurement of bone-turnover markers at 1 year corrected age.

An anti-inflammatory selective glucocorticoid receptor modulator preserves osteoblast differentiation

Glucocorticoids (GCs) are in widespread use to treat inflammatory bone diseases, such as rheumatoid arthritis (RA). Their anti-inflammatory efficacy, however, is accompanied by deleterious effects on bone, leading to GC-induced osteoporosis (GIO). These effects include up-regulation of the receptor activator of NF-κB ligand/osteoprotegerin (RANKL/OPG) ratio to promote bone-resorbing osteoclasts and include inhibition of bone-forming osteoblasts. We previously identified suppression of osteoblast differentiation by the monomer glucocorticoid receptor (GR) via the inhibition of Il11 expression as a crucial mechanism for GIO. Here we show that the GR-modulating substance compound A (CpdA), which does not induce GR dimerization, still suppresses proinflammatory cytokines in fibroblast-like synovial cells from patients with RA and in osteoblasts. In contrast to the full GR agonist dexamethasone, it does not unfavorably alter the RANKL/OPG ratio and does not affect Il11 expression and subsequent STAT3 phosphorylation in these cells. Notably, while dexamethasone inhibits osteoblast differentiation, CpdA does not affect osteoblast differentiation in vitro and in vivo. We describe here for the first time that selective GR modulators can act against inflammation, while not impairing osteoblast differentiation.

Dissociation of osteogenic and immunological effects by the selective glucocorticoid receptor agonist, compound A, in human bone marrow stromal cells

Glucocorticoids (GCs) regulate various physiological processes, including bone remodeling. Whereas physiological amounts of GCs are required for proper human osteoblast differentiation, prolonged exposure to GCs leads to substantial bone loss in vivo predominantly by inhibiting osteoblast functions. Compound A (CpdA) is a novel GC receptor modulator with the potential of an improved benefit/risk profile. Here we tested the osteoimmunological effects of CpdA on primary human osteoblasts and their paracrine interactions with osteoclasts. To assess the antiinflammatory potential of CpdA in human bone marrow stromal cell (BMSC)-derived osteoblasts, cells were stimulated with lipopolysaccharide and cytokine expression was determined. Similar to dexamethasone (DEX), CpdA profoundly suppressed lipopolysaccharide-induced TNF-α (-63%), IL-1β (-38%), and IL-6 (-36%) (P < 0.05) mRNA levels. Of note, CpdA failed to induce osteogenic differentiation of BMSCs, whereas DEX and budesonide enhanced matrix mineralization an d increased runt-related transcription factor 2 and alkaline phosphatase mRNA levels up to 5-fold in a dose-dependent manner. Interestingly, each substance promoted cell proliferation by 7-10% and suppressed apoptosis by 25-30% at low concentrations and early differentiation stages, whereas high concentrations (1 μm) suppressed proliferation and stimulated apoptosis in mature osteoblasts. Finally, CpdA did not increase the receptor activator of nuclear factor-κB ligand to osteoprotegerin mRNA ratio as compared with DEX and did not stimulate the formation of osteoclasts in coculture with BMSCs. In summary, CpdA displays dissociated osteogenic and immunological effects in human BMSCs that are distinct from those of conventional GCs. Whether the specific osteoimmunological profile of CpdA translates into a relevant in vivo effect needs to be further explored.

Glucocorticoids are not always deleterious for bone

A 23-year-old man with the rare sclerosing bone disorder van Buchem disease presented with progressively worsening headaches that eventually became persistent and associated with papilledema. Increased intracranial pressure was diagnosed, and the patient had a ventriculoperitoneal drain inserted as well as simultaneously receiving treatment with prednisone. Before starting treatment, there was biochemical evidence for increased bone turnover and for steady increases in bone mineral density (BMD) at the spine and total hip despite the patient having reached his peak height of 197 cm at the age of 19 years. Treatment with prednisone for 2 years resulted in biochemical and histologic suppression of bone formation as well as of bone resorption and arrest of further bone accumulation. Our data suggest that glucocorticoids (GCs) may represent an attractive alternative to the high-risk surgical approaches used in the management of patients with progressive sclerosing bone disorders. Our findings also suggest that whereas sclerostin may not be required for the action of GCs on bone formation, it may well be important for the action of GCs on bone resorption. The exact mechanism by which sclerostin may be involved in the regulation of bone resorption is as yet to be explored.

Selective Glucocorticoid Receptor modulators

The ancient two-faced Roman god Janus is often used as a metaphor to describe the characteristics of the Glucocorticoid Receptor (NR3C1), which exhibits both a beneficial side, that serves to halt inflammation, and a detrimental side responsible for undesirable effects. However, recent developments suggest that the Glucocorticoid Receptor has many more faces with the potential to express a range of different functionalities, depending on factors that include the tissue type, ligand type, receptor variants, cofactor surroundings and target gene promoters. This behavior of the receptor has made the development of safer ligands, that trigger the expression program of only a desirable subset of genes, a real challenge. Thus more knowledge-based fundamental research is needed to ensure the design and development of selective Glucocorticoid Receptor modulators capable of reaching the clinic. Recent advances in the characterization of novel selective Glucocorticoid Receptor modulators, specifically in the context of anti-inflammatory strategies, will be described in this review.

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.

Pharmacological strategies for improving the efficacy and therapeutic ratio of glucocorticoids in inflammatory lung diseases

Glucocorticoids are widely used to treat various inflammatory lung diseases. Acting via the glucocorticoid receptor (GR), they exert clinical effects predominantly by modulating gene transcription. This may be to either induce (transactivate) or repress (transrepress) gene transcription. However, certain individuals, including those who smoke, have certain asthma phenotypes, chronic obstructive pulmonary disease (COPD) or some interstitial diseases may respond poorly to the beneficial effects of glucocorticoids. In these cases, high dose, often oral or parental, glucocorticoids are typically prescribed. This generally leads to adverse effects that compromise clinical utility. There is, therefore, a need to enhance the clinical efficacy of glucocorticoids while minimizing adverse effects. In this context, a long-acting beta(2)-adrenoceptor agonist (LABA) can enhance the clinical efficacy of an inhaled corticosteroid (ICS) in asthma and COPD. Furthermore, LABAs can augment glucocorticoid-dependent gene expression and this action may account for some of the benefits of LABA/ICS combination therapies when compared to ICS given as a monotherapy. In addition to metabolic genes and other adverse effects that are induced by glucocorticoids, there are many other glucocorticoid-inducible genes that have significant anti-inflammatory potential. We therefore advocate a move away from the search for ligands of GR that dissociate transactivation from transrepression. Instead, we submit that ligands should be functionally screened by virtue of their ability to induce or repress biologically-relevant genes in target tissues. In this review, we discuss pharmacological methods by which selective GR modulators and "add-on" therapies may be exploited to improve the clinical efficacy of glucocorticoids while reducing potential adverse effects.

Therapeutic implications of osteoprotegerin

Osteoprotegerin (OPG), a member of the tumor necrosis factor (TNF) receptor superfamily, contributes determinatively to the bone remodeling as well as to the pathogenetic mechanism of bone malignancies and disorders of mineral metabolism. There is additional evidence that OPG can promote cell survival by inhibiting TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. A number of recent in vitro, in vivo and clinical studies have defined the role of the RANK/RANKL/OPG pathway in skeletal and vascular diseases. These works were the milestone of the deep understanding of the mechanism of OPG. This review provides an overview of the potential innovative therapeutic strategies of OPG in metastatic breast and prostate carcinoma, multiple myeloma, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis and rheumatoid arthritis. Special reference is given to the increasing evidence that RANKL and OPG may link the skeletal with the vascular system.

Minireview: live and let die: molecular effects of glucocorticoids on bone cells

Glucocorticoids (GCs) are efficient drugs that are used to treat various immune-mediated diseases, but their long-term administration is associated with multiple metabolic side effects, including osteoporosis. Molecular analyses of the mechanisms exerted by the GC receptor have resulted in the development of GC receptor agonists that selectively repress or activate GC target genes. This review summarizes the cellular and molecular effects of GCs on bone cells and highlights the critical signaling pathways that may evolve into future therapeutic strategies.

Minireview: latest perspectives on antiinflammatory actions of glucocorticoids

Taking into consideration that glucocorticoid (GC) hormones have been used clinically for over half a century and that more than 20 yr have passed since the cloning of the GC receptor (GR), it is hard to imagine that novel aspects in the molecular mechanism by which GCs mediate their antiinflammatory actions are still being unveiled today. Partly, this is because almost on a daily basis, novel insights arise from parallel fields, e.g. nuclear receptor cofactor and chromatin regulation and their concomitant impact on gene transcription events, eventually leading to a revisitation or refinement of old hypotheses. On the other hand, it does remain striking and puzzling why GCs use different mechanisms in so many different cell types and on many different target genes to elicit an antiinflammatory effect. Meanwhile, the obvious question for the clinic remains: is the separation of GR functionalities through differential ligand design the strategy of choice to avoid most GC-mediated side effects? This minireview aims to highlight some of the latest findings on aspects of the antiinflammatory working mechanisms of GCs.

The combination of bortezomib, melphalan, dexamethasone and intermittent thalidomide is an effective regimen for relapsed/refractory myeloma and is associated with improvement of abnormal bone metabolism and angiogenesis

This phase 2 study aimed to determine the efficacy and safety of the combination of bortezomib, melphalan, dexamethasone and intermittent thalidomide (VMDT) and its effect on bone remodeling and angiogenesis in relapsed/refractory myeloma. Bortezomib (1.0 mg/m(2)) was given on days 1, 4, 8, 11, oral melphalan (0.15 mg/kg) on days 1-4, whereas thalidomide (100 mg per day) and dexamethasone (12 mg/m(2)) were administered on days 1-4 and 17-20 of a 28-day cycle, for four cycles. Patients without disease progression continued for up to eight cycles. VMDT effect on bone remodeling was evaluated by measuring osteoclast regulators (soluble receptor activator of nuclear factor-kappa B ligand/osteoprotegerin ratio, osteopontin, macrophage inflammatory protein-1alpha), dickkopf-1 protein, bone resorption and formation markers, whereas its effect on angiogenesis was assessed by measuring serum vascular endothelial growth factor, angiogenin, angiopoietin-2 and basic fibroblast growth factor, after four cycles and at the study end. A total of 62 patients were enrolled. The overall response rate was 66%: CR 13%, vgPR 27% and PR 26%. Median time to response was 35 days and median time to progression was 9.3 months. Common adverse events included cytopenias, peripheral neuropathy and infections. No patient experienced deep-vein thrombosis. VMDT reduced angiogenic cytokines, osteoclast regulators, dickkopf-1 and bone resorption. We conclude that VMDT with intermittent thalidomide is an active and well-tolerated regimen for relapsed/refractory myeloma, affecting abnormal bone remodeling and angiogenesis.

Nuclear receptor drug discovery

Nuclear receptors (NR) are ligand-activated transcription factors that regulate the activation of a variety of important target genes. There are 48 genes that encode NRs in the human genome, and these receptors now represent one of the most important targets for therapeutic drug development. Successful identification of selective NR modulators has transformed the NR drug discovery strategy from the designing of synthetic compounds that mimic the full function of cognate ligands to developing compounds that selectively modulate the functional activity of an NR in a manner that is distinct from the cognate ligands. Current efforts regarding NR drug development continue to focus on improving the function and tissue selectivity of drug candidates to reduce undesirable side effects. This review focuses on modulators of the glucocorticoid receptor (GR), androgen receptor (AR), and pregnane X receptor (PXR).

Drug insight: selective agonists and antagonists of the glucocorticoid receptor

Glucocorticoid hormones exert a wide spectrum of metabolic and immunological effects. They function through the glucocorticoid receptor, a member of the nuclear receptor superfamily. Glucocorticoids are particularly effective as anti-inflammatory agents but often cause severe side effects. The structure of the ligand-binding domain of the glucocorticoid receptor has now been elucidated, and a series of studies have shown that even subtle changes to the ligand structure alter the final conformation of the ligand-receptor complex, with consequences for both protein recruitment and the function of the receptor. This has led to concerted efforts to find selective ligands for the glucocorticoid receptor that preserve the beneficial anti-inflammatory activity but reduce the side-effect profile. The direct health-care benefits of such a simple, safe, orally active agent targeting the underlying inflammatory process in, for example, rheumatoid arthritis would be considerable in terms of reduced patient suffering; furthermore, the indirect benefits in terms of reducing the costs of therapeutic delivery and preventing loss of productivity would be even greater.

Receptor activator of nuclear factor kappaB ligand and osteoprotegerin regulation of bone remodeling in health and disease

Osteoclasts and osteoblasts dictate skeletal mass, structure, and strength via their respective roles in resorbing and forming bone. Bone remodeling is a spatially coordinated lifelong process whereby old bone is removed by osteoclasts and replaced by bone-forming osteoblasts. The refilling of resorption cavities is incomplete in many pathological states, which leads to a net loss of bone mass with each remodeling cycle. Postmenopausal osteoporosis and other conditions are associated with an increased rate of bone remodeling, which leads to accelerated bone loss and increased risk of fracture. Bone resorption is dependent on a cytokine known as RANKL (receptor activator of nuclear factor kappaB ligand), a TNF family member that is essential for osteoclast formation, activity, and survival in normal and pathological states of bone remodeling. The catabolic effects of RANKL are prevented by osteoprotegerin (OPG), a TNF receptor family member that binds RANKL and thereby prevents activation of its single cognate receptor called RANK. Osteoclast activity is likely to depend, at least in part, on the relative balance of RANKL and OPG. Studies in numerous animal models of bone disease show that RANKL inhibition leads to marked suppression of bone resorption and increases in cortical and cancellous bone volume, density, and strength. RANKL inhibitors also prevent focal bone loss that occurs in animal models of rheumatoid arthritis and bone metastasis. Clinical trials are exploring the effects of denosumab, a fully human anti-RANKL antibody, on bone loss in patients with osteoporosis, bone metastasis, myeloma, and rheumatoid arthritis.

Functions of RANKL/RANK/OPG in bone modeling and remodeling

The discovery of the RANKL/RANK/OPG system in the mid 1990s for the regulation of bone resorption has led to major advances in our understanding of how bone modeling and remodeling are regulated. It had been known for many years before this discovery that osteoblastic stromal cells regulated osteoclast formation, but it had not been anticipated that they would do this through expression of members of the TNF superfamily: receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG), or that these cytokines and signaling through receptor activator of NF-kappaB (RANK) would have extensive functions beyond regulation of bone remodeling. RANKL/RANK signaling regulates osteoclast formation, activation and survival in normal bone modeling and remodeling and in a variety of pathologic conditions characterized by increased bone turnover. OPG protects bone from excessive resorption by binding to RANKL and preventing it from binding to RANK. Thus, the relative concentration of RANKL and OPG in bone is a major determinant of bone mass and strength. Here, we review our current understanding of the role of the RANKL/RANK/OPG system in bone modeling and remodeling.

Expeditious synthesis of steroids containing a 2-methylsulfanyl-acetyl side chain as potential glucocorticoid receptor imaging agents

In our effort to develop imaging agents for brain glucocorticoid receptors, we have prepared several novel glucocorticoids possessing a 2-methylsulfanyl-acetyl side chain. The synthesis was accomplished via a Mitsunobu reaction with thiobenzoic acid starting from cortisol, prednisolone, dexamethasone and triamcinolone acetonide to give the corresponding S-thiobenzoates in 75-82% yield. Subsequent saponification and reaction with methyl iodide afforded C-21 methylthioethers in 68-82% yield. All compounds were tested in an in vitro glucocorticoid receptor-binding assay. Triamcinolone acetonide-based compound 12 showed promising binding affinity of 144% relative to dexamethasone (100%). Compound 12 was selected for radiolabeling with the short-lived positron emitter carbon-11. The radiolabeling was carried out starting from S-thiobenzoate 8 and in situ formation of the corresponding sodium thiolate, which was further reacted with [(11)C]methyl iodide. The obtained radiochemical yield was 20-30%. The specific activity was determined to be 20-40GBq/micromol at the end-of-synthesis, and the radiochemical purity exceeded 98%.

Corticosteroid-induced adverse events in adults: frequency, screening and prevention

Corticosteroids represent the most important and frequently used class of anti-inflammatory drugs and are the reference therapy for numerous neoplastic, immunological and allergic diseases. However, their substantial efficacy is often counter-balanced by multiple adverse events. These corticosteroid-induced adverse events represent a broad clinical and biological spectrum from mild irritability to severe and life-threatening adrenal insufficiency or cardiovascular events. The purpose of this article is to provide an overview of the available data regarding the frequency, screening and prevention of the adverse events observed in adults during systemic corticosteroid therapy (topically administered corticosteroids are outside the remit of this review). These include clinical (i.e. adipose tissue redistribution, hypertension, cardiovascular risk, osteoporosis, myopathy, peptic ulcer, adrenal insufficiency, infections, mood disorders, ophthalmological disorders, skin disorders, menstrual disorders, aseptic necrosis, pancreatitis) and biological (i.e. electrolytes homeostasis, diabetogenesis, dyslipidaemia) events. Lastly, data about the prescription of corticosteroids during pregnancy are provided. This review underscores the absence of data on many of these adverse events (e.g. lipodystrophy, dyslipidaemia). Our intent is to present to practitioners data that can be used in a practical way to both screen and prevent most of the adverse events observed during systemic corticosteroid therapy.

Selective glucocorticoid receptor agonists (SEGRAs): novel ligands with an improved therapeutic index

Glucocorticoids are among the most successful therapies in the treatment of chronic inflammatory and autoimmune diseases. Their efficacy seems to be caused by the interference of the ligand-activated glucocorticoid receptor with many pro-inflammatory pathways via different mechanisms. The ubiquitous expression of the glucocorticoid receptor is a prerequisite for efficacy. Their main drawback, however, is due to their potential to induce adverse effects, in particular upon high dosage and prolonged usage. For the purpose reducing systemic side effects, topical glucocorticoids that act locally have been developed. Nevertheless, undesirable cutaneous effects such as skin atrophy persist from the use of topical glucocorticoids. Therefore a high medical need exists for drugs as effective as glucocorticoids but with a reduced side effect profile. Glucocorticoids function by binding to and activating the glucocorticoid receptor which positively or negatively regulates the expression of specific genes. Several experiments suggest that negative regulation of gene expression by the glucocorticoid receptor accounts for its anti-inflammatory action. This occurs through direct or indirect binding of the receptor to pro-inflammatory transcription factors that are already bound to their regulatory sites. The positive action of the receptor occurs through homodimer binding of the ligand receptor complex to discrete nucleotide sequences and this contributes to some of the adverse effects of the hormone. Glucocorticoid receptor ligands that promote the negative regulatory action of the receptor with reduced positive regulatory function should therefore show an improved therapeutic index. A complete separation of the positive from the negative regulatory activities of the receptor has so far not been possible because of the interdependent nature of the two regulatory processes. Nevertheless, recent understanding of the molecular mechanisms of the GR has triggered several drug discovery programs and these have led to the identification of dissociated GR-ligands. Such selective GR agonists (SEGRAs) are likely to enter clinical testing soon.

An update on glucocorticoid-induced osteoporosis

PURPOSE OF REVIEW

Glucocorticoids are widely used, often long term, and a major side effect is osteoporosis and increased risk of fracture. This review considers how common is the problem, the patients who are most at risk, our current understanding of mechanisms, and how to prevent and effectively treat glucocorticoid-induced osteoporosis. The actions currently being undertaken in clinical practice are reviewed.

RECENT FINDINGS

Glucocorticoid-induced osteoporosis is an increasing problem that occurs not only in those on high-dose therapy. Advances in our knowledge of the cellular and cytokine mechanisms of bone turnover and glucocorticoid mechanisms of action are leading to a better understanding of how glucocorticoids affect bone cells and novel ways of prevention. Although there are effective treatments to prevent and control glucocorticoid-induced osteoporosis as well as guidelines for their use, they are still not being applied in routine clinical practice.

SUMMARY

Glucocorticoid-induced osteoporosis is a significant problem. Although our understanding of effective prevention and treatment strategies is improving, there needs to be better implementation of these strategies.

Differential expression of receptor activator of nuclear factor-?B ligand and osteoprotegerin mRNA in periodontal diseases

BACKGROUND AND OBJECTIVE

Receptor activator of nuclear factor-kappaB ligand (RANKL) is responsible for the induction of osteoclastogenesis and bone resorption, whereas its decoy receptor, osteoprotegerin, can directly block this action. Because this dyad of cytokines is crucial for regulating the bone remodelling process, imbalances in their expression may cause a switch from the physiological state to enhanced bone resorption or formation. This study investigated the mRNA expression of RANKL and osteoprotegerin, as well as their relative ratio, in the gingival tissues of patients with various forms of periodontal diseases.

MATERIAL AND METHODS

Gingival tissue was obtained from nine healthy subjects and 41 patients, who had gingivitis, chronic periodontitis, generalized aggressive periodontitis, and chronic periodontitis and were receiving immunosuppressant therapy. Quantitative real-time polymerase chain reaction was employed to evaluate the mRNA expression of RANKL and osteoprotegerin in these tissues.

RESULTS

Compared with healthy individuals, patients in all periodontitis groups, but not those with gingivitis, exhibited stronger RANKL expression and a higher relative RANKL/osteoprotegerin ratio. In addition, osteoprotegerin expression was weaker in patients with chronic periodontitis. When patients with generalized aggressive periodontitis and chronic periodontitis were compared, the former exhibited stronger RANKL expression, whereas the latter exhibited weaker osteoprotegerin expression, and there was no difference in their relative ratio. When chronic periodontitis patients were compared with chronic periodontitis patients receiving immunosuppressant therapy, osteoprotegerin, but not RANKL, expression was stronger in the latter.

CONCLUSION

This study demonstrates that RANKL and osteoprotegerin expression are differentially regulated in various forms of periodontitis, and the relative RANKL/osteoprotegerin ratio appears to be indicative of disease occurrence. This information may confer diagnostic and therapeutic value in periodontitis.

Separating transrepression and transactivation: a distressing divorce for the glucocorticoid receptor?

Glucocorticoids (corticosteroids) are highly effective in combating inflammation in the context of a variety of diseases. However, clinical utility can be compromised by the development of side effects, many of which are attributed to the ability of the glucocorticoid receptor (GR) to induce the transcription of, or transactivate, certain genes. By contrast, the anti-inflammatory effects of glucocorticoids are due largely to their ability to reduce the expression of pro-inflammatory genes. This effect has been predominantly attributed to the repression of key inflammatory transcription factors, including AP-1 and NF-kappaB, and is termed transrepression. The ability to functionally separate these transcriptional functions of GR has prompted a search for dissociated GR ligands that can differentially induce transrepression but not transactivation. In this review, we present evidence that post-transcriptional mechanisms of action are highly important to the anti-inflammatory actions of glucocorticoids. Furthermore, we present the case that mechanistically distinct forms of glucocorticoid-inducible gene expression are critical to the development of anti-inflammatory effects by repressing inflammatory signaling pathways and inflammatory gene expression at multiple levels. Considerable care is therefore required to avoid loss of anti-inflammatory effectiveness in the development of novel transactivation-defective ligands of GR.

Skeletal remodeling in health and disease

The use of genetically manipulated mouse models, gene and protein discovery and the cataloguing of genetic mutations have each allowed us to obtain new insights into skeletal morphogenesis and remodeling. These techniques have made it possible to identify molecules that are obligatory for specific cellular functions, and to exploit these molecules for therapeutic purposes. New insights into the pathophysiology of diseases have also enabled us to understand molecular defects in a way that was not possible a decade ago. This review summarizes our current understanding of the carefully orchestrated cross-talk between cells of the bone marrow and between bone cells and the brain through which bone is constantly remodeled during adult life. It also highlights molecular aberrations that cause bone cells to become dysfunctional, as well as therapeutic options and opportunities to counteract skeletal loss.

Gingival crevicular fluid levels of RANKL and OPG in periodontal diseases: implications of their relative ratio

AIM

Receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) are a system of molecules that regulate bone resorption. This study aims to compare the levels of RANKL, OPG and their relative ratio in gingival crevicular fluid (GCF) of healthy and periodontal disease subjects.

MATERIAL AND METHODS

GCF was obtained from healthy (n=21), gingivitis (n=22), chronic periodontitis (n=28), generalized aggressive periodontitis (n=25) and chronic periodontitis subjects under immunosuppressant therapy (n=11). RANKL and OPG concentrations in GCF were measured by enzyme-linked immunosorbent assays.

RESULTS

RANKL levels were low in health and gingivitis groups, but increased in all three forms of periodontitis. OPG levels were higher in health than all three periodontitis, or gingivitis groups. There were no differences in RANKL and OPG levels between chronic and generalized aggressive periodontitis groups, whereas these were lower in the immunosuppressed chronic periodontitis group. The RANKL/OPG ratio was significantly elevated in all three periodontitis forms, compared with health or gingivitis, and positively correlated to probing pocket depth and clinical attachment level.

CONCLUSION

GCF RANKL and OPG levels were oppositely regulated in periodontitis, but not gingivitis, resulting in an enhanced RANKL/OPG ratio. This ratio was similar in all three periodontitis groups and may therefore predict disease occurrence.

Levels of bone collagen markers in preterm infants: relation to antenatal glucocorticoid treatment

Although the beneficial effects of antenatally administered glucocorticoids are well documented, data on the potential of adverse consequences are limited. The objective of this study was to determine the effects of antenatally administered glucocorticoids on biochemical markers of bone metabolism of 55 preterm infants with a gestational age of 24-34 weeks who were enrolled in the study. Neonates were divided into two groups according to antenatal exposure to corticosteroids. There were no significant differences between the groups in clinical characteristics and anthropometric variables. We studied blood levels of osteocalcin (OC), carboxy-terminal propeptide of type I procollagen (PICP), and carboxy-terminal telopeptide of type I collagen (ICTP) at the time of delivery, on postnatal day 10, and at 2 and 4 months of life. Comparing the groups, we found statistically significant reduction in PICP levels at birth in corticosteroid-exposed neonates (P < 0.05). The levels of bone markers increased progressively on the first days of life. There were no significant differences between groups in bone markers at 10 days or at 2 and 4 months of life. We found no significant difference for bone markers between groups of infants exposed to single or repeated maternal corticosteroid treatments. In summary, antenatal glucocorticoid treatments are suggested to have a negative impact on fetal bone formation as reflected by low PICP levels at birth. However, this negative effect on bone markers seems to be a temporary effect that subsides on the first days of life and afterward.

Modelling the glucocorticoid receptor and producing therapeutic agents with anti-inflammatory effects but reduced side-effects

Glucocorticoid hormones exert a wide spectrum of metabolic and immunological effects. They are synthesized from a cholesterol precursor and are structurally related to the other steroid hormones, progesterone, aldosterone and oestrogen. They act through the glucocorticoid receptor (GR), a member of the nuclear receptor superfamily. The GR is an intracellular receptor; the hydrophobic ligand accesses its receptor by diffusion across the plasma membrane. The ligand-activated GR translocates to the nucleus to regulate expression of its target genes. The GR, in common with the rest of the receptor family, can be functionally divided into an N-terminal transcription activation domain, a central DNA binding domain and a C-terminal ligand binding domain, which also includes a second transactivation domain. Although synthetic glucocorticoids are the most potent anti-inflammatory agents known, their use is limited owing to the range and severity of their side-effects. The structure of the ligand binding domain of the glucocorticoid receptor has now been solved, and a series of studies has shown that even subtle changes to the ligand structure alter the final conformation of the ligand-receptor complex, with consequences for further protein recruitment and for the function of the receptor. This, coupled with the successful development of selective oestrogen receptor agonists, has led to concerted efforts to find selective GR ligands, with preserved beneficial anti-inflammatory activity, but reduced side-effect profile. Current efforts have identified several useful tool compounds, and further molecules are in development in several pharmaceutical companies.

Insight into the molecular mechanisms of glucocorticoid receptor action promotes identification of novel ligands with an improved therapeutic index

Glucocorticoids are highly effective in the therapy of inflammatory and autoimmune disorders. Their beneficial action is restricted because of their adverse effects upon prolonged usage. Topical glucocorticoids that act locally have been developed to significantly reduce systemic side effects. Nonetheless, undesirable cutaneous effects such as skin atrophy persist from the use of topical glucocorticoids. There is therefore a high medical need for drugs as effective as glucocorticoids but with a reduced side-effect profile. Glucocorticoids function by binding to and activating the glucocorticoid receptor that positively or negatively regulates the expression of specific genes. Several experiments suggest that the negative regulation of gene expression by the glucocorticoid receptor accounts for its anti-inflammatory action. This occurs through direct or indirect binding of the receptor to transcription factors such as activator protein-1, nuclear factor-kappaB or interferon regulatory factor-3 that are already bound to their regulatory sites. The positive action of the receptor occurs through homodimer binding of the receptor to discrete nucleotide sequences and this possibly contributes to some of the adverse effects of the hormone. Glucocorticoid receptor ligands that promote the negative regulatory action of the receptor with reduced positive regulatory function should therefore show improved therapeutic potential. A complete separation of the positive from the negative regulatory activities of the receptor has so far not been possible because of the interdependent nature of the two regulatory processes. Nevertheless, considerable improvement in the therapeutic action of glucocorticoid receptor ligands is being achieved through the use of key molecular targets for screening novel glucocorticoid receptor ligands.