Inhibitory Action Of Dexamethasone Research Articles

Mechanism of glucocorticoid protection of airway smooth muscle from proasthmatic effects of long-acting β2-adrenoceptor agonist exposure

Chronic use of long-acting beta2-adrenergic receptor agonists (LABAs), resulting in beta2-adrenergic receptor desensitization, has been associated with increased asthma morbidity. When LABAs are used in combination with inhaled glucocorticoids, however, asthma control is improved, raising the following question: Do glucocorticoids inhibit the proasthmatic mechanism that mediates altered contractility in LABA-exposed airway smooth muscle (ASM)? This study aimed to identify the potential protective role and mechanism of action of glucocorticoids in mitigating the effects of prolonged LABA exposure on ASM constrictor and relaxation responsiveness. Cultured human ASM cells and isolated rabbit ASM tissues were examined for induced changes in agonist-mediated cyclic adenosine monophosphate accumulation, constrictor and relaxation responsiveness, and expression of specific glucocorticoid-regulated molecules after 24-hour exposure to the LABA salmeterol in the absence and presence of dexamethasone. Salmeterol-exposed ASM exhibited impaired cyclic adenosine monophosphate and relaxation responses to isoproterenol and increased acetylcholine-induced contractility. These proasthmatic effects of prolonged LABA exposure were attributed to upregulated phosphodiesterase 4 (PDE4) activity and were ablated by pretreatment with dexamethasone. Further studies demonstrated that (1) dexamethasone suppressed activation of the mitogen-activated protein kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2), which upregulate PDE4 expression in salmeterol-exposed ASM; and (2) the inhibitory actions of dexamethasone on salmeterol-induced ERK1/2 activation and resultant PDE4-mediated changes in ASM responsiveness were prevented by gene silencing or pharmacologic inhibition of dexamethasone-induced expression of mitogen-activated protein kinase phosphatase 1, an endogenous deactivator of ERK1/2 signaling. Glucocorticoids prevent the adverse proasthmatic effects of prolonged LABA exposure on airway responsiveness as a result of glucocorticoid-induced upregulation of mitogen-activated protein kinase phosphatase 1, which inhibits proasthmatic ERK1/2 signaling in the LABA-exposed ASM.

An in-silico model of the biosynthesis of neurotransmitter glutamate, elucidates the complex regulatory role of glucocorticoids in neurotransmitter glutamate release

An in-silico model, of the glucocorticoid regulated glutamate release, in rat hippocampal tissue, is constructed. The model permits the pseudo-steady state estimation of various fluxes, experimentally impossible to measure, from a set of measured rates. Estimates of the astrocytic pyruvate carboxylase reaction and the neuronal TCA cycle rates are correlated with different dexamethasone concentrations, in order to extrapolate explicit kinetic equations. The model suggests that the observed effects of glucocorticoids can be attributed to the inhibitory actions of dexamethasone on two competing pathways, that of the neuronal TCA cycle and the biosynthetic pathway of neurotransmitter glutamate.

Functional Interference of Dexamethasone on Some Morphine Effects:Hypothesis for the Steroid-Opioid Interaction

The effect of dexamethasone (DEX) and its interaction with morphine has been studied on transmurally-stimulated guinea-pig ileum preparation, gastrointestinal transit and analgesia. TRANSMURALLY-STIMULATED GUINEA-PIG ILEUM PREPARATION: DEX dose-dependently reduced the contractions of the ileum. Proteic synthesis inhibitors did not modify the inhibition induced by DEX whereas RU-38486, a glucocorticoid antagonist receptor, antagonized completely the inhibitory effect of DEX. GASTROINTESTINAL TRANSIT: DEX was found to antagonize morphine-, atropine- and verapamil-induced constipation. Cycloheximide does not modify the DEX effects. RU-38486 reverses both the inhibitory action of DEX on gastrointestinal transit and its reducing effect on morphine-induced constipation. DEX reduced the antinociception induced by mu agonists, morphine, DAMGO and beta endorphin whereas the steroid exerted little or no influence on the antinociception induced by a delta1 agonist, DPDPE and delta2 agonist deltorphin II. DEX potentiated the antinociception induced by the K agonist, U50,488. Cycloheximide, a protein synthesis inhibitor, prevented the antagonism by DEX of responses to the mu opioid agonists. Finally, i.c.v. injection of DEX significantly reduced morphine analgesia in Swiss mice whereas no effects were observed in DBA/2J and C57BL/6 mice. In addition, i.p. injection of DEX significantly reduced morphine analgesia in all three strains. Our data indicate that in the rodent brain there is an important functional interaction between the corticosteroid and the opioid systems at least at the mu. receptor level, while delta and K receptors are modulated in different ways. These results, particularly the effects of drug interaction for i.c.v. administration, strongly confirm a central site for DEX and RU 38486 action as well as the use of different genetic strains may provide a useful approach for studying DEX-morphine analgesia interaction.

IGF-I signalling in bone growth: Inhibitory actions of dexamethasone and IL-1β

Objective To determine if glucocorticoids and proinflammatory cytokines inhibit bone growth through a common mechanism involving impaired IGF-I signalling. Design IGF-I (100 ng/ml), dexamethasone (dex) (10 −6 M) and IL-1β (10 ng/ml) with inhibitors of the PI3K (LY294002) and Erk 1/2 (PD98059 and UO126) IGF-I pathways (all 10 μM) were studied using the ATDC5 chondrocyte cell line and murine fetal metatarsal cultures. Results IGF-I stimulated ATDC5 chondrocyte proliferation (322%; P < 0.001 versus control). Addition of PD or LY individually to IGF-I supplemented ATDC5 cultures partially reduced proliferation by 32% ( P < 0.001), and 66% ( P < 0.001), respectively. PD and LY in combination blocked all IGF-I stimulated ATDC5 proliferation. LY significantly reversed IGF-I stimulatory effects on metatarsal growth ( P < 0.001), whereas PD and UO treatment had no effect. IGF-I induced ATDC5 proliferation was further decreased when Dex (24%; P < 0.01) or IL-1β (33%; P < 0.001) were added to PD but not LY cultures. Metatarsal growth inhibition by LY was unaltered by Dex or IL-1β addition. Conclusions Both the PI3K and Erk 1/2 pathways contributed independently to IGF-I mediated ATDC5 proliferation. However in metatarsal cultures, the Erk 1/2 pathway was not required for IGF-I stimulated growth. Dex and IL-1β may primarily inhibit IGF-I induced bone growth through the PI3K pathway.

The anti-inflammatory effect of glucocorticoids is mediated by glucocorticoid-induced leucine zipper in epithelial cells

Nuclear factor kappaB (NF-kappaB) plays a key role in the pathogenesis of asthma, being linked to the production of inflammatory cytokines that drive inflammation. A recently described anti-inflammatory protein, glucocorticoid-induced leucine zipper (GILZ), interferes with NF-kappaB-mediated gene transcription in T cells and macrophages. We sought to analyze the regulation of GILZ expression in airway epithelial cells and determine whether GILZ mediates part of the anti-inflammatory effect of corticosteroids. GILZ expression was assessed by means of PCR and immunoblotting in human epithelial cells at baseline and after stimulation with dexamethasone or cytokines (IL-1beta, TNF-alpha, and IFN-gamma). The effect of GILZ on LPS-, IL-1beta-, and polyinosinic:polycytidylic acid-induced NF-kappaB activation was assessed in BEAS-2B cells overexpressing GILZ. The requirement for GILZ in the inhibitory action of dexamethasone was assessed by knocking down GILZ expression by means of small interfering RNA (siRNA) technology. GILZ is constitutively expressed by human airway epithelial cells, and its levels are increased by dexamethasone and decreased by inflammatory cytokines. Overexpression of GILZ in BEAS-2B cells significantly inhibited the ability of IL-1beta, LPS, and polyinosinic:polycytidylic acid to activate NF-kappaB, whereas knockdown of GILZ inhibited the ability of dexamethasone to suppress IL-1beta-induced chemokine expression. This study demonstrates the expression of GILZ in human airway epithelial cells, its induction by dexamethasone, its suppression by inflammatory cytokines, and its role in mediating the anti-inflammatory effects of dexamethasone. Therapeutic upregulation of GILZ may be a novel strategy for the treatment of asthma.

Inhibitory effects of glucocorticoids on TGF-β-Smad 3 signalling are activated by tauroursodeoxycholic acid in hepatic stellate cells

Aims: Tauroursodeoxycholic acid (TUDCA) has a positive effect on cholestatic liver disease especially with autoimmune aspects, which seems to be enhanced by a combination with locally active corticosteroids. TGF-β-Smad 3 signalling activates hepatic stellate cells (HSC) and promotes the development of liver fibrosis. A TGF-β dimer forms a complex with the type II and type I receptor and transduces the signal via Smads into the cell nucleus. Our recent studies with HSC showed that glucocorticoids and their receptor (GR) interact with the TGF-β-Smad 3 pathway, which leads to an inhibition of TGF-β effects. Aim of the present study was to investigate if TUDCA interacts with TGF-β-Smad 3 signalling and if there is any cooperation with glucocorticoids. Methods: We co-transfected a HSC derived cell line (CFSC) with a TGF-β sensitive reporter gene [(CAGA)9-MLP-luc] and a plasmid expressing a GR-Fragment (hGR418–777). Thereafter, cells were stimulated with TGF-β, or TGF-β and glucocorticoids (dexamethasone, hydrocortisone or budesonide), and all with or without TUDCA. Results: The co-treatment of CFSC with dexamethasone/budesonide and TUDCA enhance the inhibitory effect of the glucocorticoids on TGF-β induced Smad 3 signalling. Whereas inhibitory action of dexamethasone on TGF-β could be restored by mifepristone, the glucocorticoid antagonist had no influence on budesonide effect. Our data indicate that dexamethasone and budesonide bind their receptor at a separate binding site. Conversely, TUDCA alone stimulates TGF-β response in HSC, which might enhance the profibrotic effects of the cytokine in abscence of glucocorticoids. Conclusions: We conclude that oppositional effects of TUDCA on TGF-β-Smad 3 signalling are dependent on glucocorticoid presence.

Glucocorticoids inhibit vascular endothelial growth factor expression in growth plate chondrocytes

Vascular endothelial growth factor (VEGF) plays an essential role in angiogenesis in the growth plate and ultimately in regulating endochondral ossification. Since longitudinal bone growth is often disturbed in children who are treated with glucocorticoids, we investigated the effects of dexamethasone on VEGF expression by epiphyseal chondrocytes. Cells were cultured from tibial growth plates of neonatal piglets. Using Northern blotting and RT-PCR techniques, the chondrocyte-specific markers aggrecan, collagen II and CD-RAP were detected. Also the glucocorticoid receptor (GR) was expressed. VEGF protein secreted from these cells was examined by ELISA and Western immunoblotting. The VEGF 121 and VEGF 165 isoforms were detected in the supernatant. As determined by RT-PCR, all three major mRNA splice variants were produced, including the species encoding VEGF 189. Dexamethasone (100 nM) inhibited both protein and mRNA expression by approximately 45%. Hydrocortisone (cortisol) and prednisolone also inhibited VEGF secretion, but they were less active than dexamethasone. The inhibitory actions of dexamethasone were almost completely blocked by the GR antagonist Org34116, indicating that the GR mediates these actions. Degradation of the VEGF mRNA was not accelerated by dexamethasone. Therefore, a transcriptional mechanism seems likely. Downregulation of this important growth factor could lead to disruption of the normal invasion of blood vessels in the growth plate, which could contribute to disturbed endochondral ossification and growth.

Pro-inflammatory effects of cholera toxin: role of tumor necrosis factor alpha

Cholera toxin has been traditionally described as the one that does not induce inflammation. It has, however, potent adjuvant and immuno-modulatory activities. Since the adjuvanticity of other compounds is linked to their capacity to induce inflammation, in the present study the pro-inflammatory activity of cholera toxin was investigated. We studied this activity in the following rat models of inflammation: paw edema and neutrophil migration into the peritoneal cavity, and evaluated cholera toxin's effect on tumor necrosis factor alpha (TNF-α) production by mouse macrophages. We, also, explored the effects of dexamethasone (DEXA) and of two inhibitors of TNF-α production, thalidomide (TAL) and pentoxifylline, on paw swelling. Cholera toxin-induced significant and dose-dependent paw edema, which peaked 48 h after toxin challenge (Cholera toxin 2.5μg: 2.39±0.22 ml). Cholera toxin B subunit did not show edematogenic activity. DEXA, TAL and pentoxifylline significantly reduced cholera toxin-induced edema (DEXA 0.5mg/kg: 42.6% of inhibition; TAL 45mg/kg: 36% of inhibition; pentoxifylline 45mg/kg: 61% of inhibition). Neither cholera toxin nor its B subunit induced neutrophil migration into peritoneal cavities. Cholera toxin stimulated the release of TNF-α by macrophages (cholera toxin 10μg: 11.46±0.44 UI/ml). These data provide evidences that cholera toxin exhibits significant pro-inflammatory activity. It also indicates the role of TNF-α upon the pathophysiology of this event based on the inhibitory action of DEXA, TAL and pentoxifylline, and on TNF-α secretion induced by cholera toxin.

Effect of dexamethasone on the expression of p34(cdc2) and cyclin B1 in pig oocytes in vitro.

The meiotic division in oocytes is arrested in the G2 phase of the cell cycle. Resumption of meiosis, also known as oocyte maturation, entails a G2 to M transition. At the G2-M boundary, maturation promoting factor (MPF) activation is usually induced via several ways, including tyrosine dephosphorylation of p34(cdc2) and synthesis of cyclin B according to cell type and species. Previous studies in our laboratory demonstrated that glucocorticoids directly inhibit the meiotic maturation of pig oocytes in vitro. The aim of this study was therefore to investigate the influence of glucocorticoids on the expression of p34(cdc2) and cyclin B1 in resumption of meiosis of pig oocytes. We detected the relative levels and association of p34(cdc2) and cyclin B1. Isolated cumulus-enclosed oocytes were cultured in Waymouth MB752/1 medium supplemented with sodium pyruvate (50 microgram/ml), LH (0.5 microgram/ml), FSH (0.5 microgram/ml), and estradiol-17beta (1 microgram/ml) in the presence or absence of dexamethasone (DEX) for 24 hr; they then were cultured without hormonal supplements in the presence or absence of DEX for an additional 24 hr. We found that cyclin B1, as well as p34(cdc2), was already present in fully grown G2-arrested pig oocytes when removed from the follicle. In these oocytes, cyclin B1 and p34(cdc2) were already associated in complex. Treatment with DEX at concentrations of 1 microgram/ml or above decreased the level of cyclin B1, but had no effect on the level of p34(cdc2). The exposure of oocytes to DEX also decreased the amount of complexed p34(cdc2)-cyclin B1. These findings suggest that the inhibitory action of DEX on meiotic maturation could be due, at least in part, to the reduced amount of p34(cdc2)-cyclin B1 complex.

Regulation of induction of nitric oxide synthase and the inhibitory actions of dexamethasone in the human intestinal epithelial cell line, Caco-2: influence of cell differentiation.

1. The inducible isoform of nitric oxide synthase (iNOS) may be involved in the pathogenesis of inflammatory bowel disease. Using the human intestinal epithelial cell line, Caco-2, iNOS expression, regulation and sensitivity to the glucocorticoid, dexamethasone after cytokine exposure and its relationship to the degree of differentiation has been studied. 2. NOS activity, assessed by NO2- and NO3- release, was time-dependently increased after exposure to interferon gamma alone or in combination with interleukin-1beta and tumour necrosis factor alpha. 3. Cytokine-induced iNOS activity was increased with days in culture over 20 days and number of passages, suggesting iNOS up-regulation during enterocyte-like differentiation. This activity was inhibited by the selective iNOS inhibitor 1400 W (0.1 - 100 microM). In addition, iNOS protein induction was confirmed by Western blot. 4. Actinomycin D (5 microg ml(-1) inhibited cytokine-induced iNOS activity, protein expression and mRNA level. Pyrrolidine dithiocarbamate (PDTC: 10 - 200 microM) and 3,4 dichloroisocoumarin (0.1 - 100 microM) reduced cytokine-induced iNOS activity and protein expression at both day 10 and 15 after confluence. PDTC also decreased iNOS mRNA levels, suggesting NF-kappaB involvement in its transcription at these times. 5. The tyrphostins A25 and B42 reduced cytokine-induced iNOS activity at both day 10 and 15 after confluence, indicating the JAK-2 kinase is also involved at these times. The tyrphostins also reduced the iNOS protein expression. 6. Dexamethasone (0.1 - 10 microM, for 24 h) reduced cytokine-induced iNOS activity at day 15 and 20 after cell confluence, but not at day 5 or 10. 7. Dexamethasone (5 microM) decreased cytokine-induced iNOS protein expression at day 10 as well as at day 15 after confluence. 8. These findings indicate that iNOS induction and its inhibition by dexamethasone in this human intestinal epithelial cell line is dependent on the degree of differentiation.

Pituitary adenylate cyclase-activating polypeptide, interleukin-6 and glucocorticoids regulate the release of vascular endothelial growth factor in pituitary folliculostellate cells

There is increasing evidence that hormones play an important role in the control of endothelial cell function and growth by regulating the production of vascular endothelial growth factor (VEGF). VEGF regulates vascular permeability and represents the most powerful growth factor for endothelial cells. In the normal anterior pituitary, VEGF has been detected only in folliculostellate (FS) cells. In the present study, the regulation of the release of VEGF from FS-like mouse TtT/GF cells, and from FS cells of rat pituitary monolayer cell cultures was investigated using a specific VEGF ELISA. Basal release of VEGF was demonstrated in cultures of both TtT/GF cells and rat pituitary cells. Interestingly, the VEGF secretion was stimulated by both forms of pituitary adenylate cyclase-activating polypeptide (PACAP-38 and PACAP-27), indicating that this hypothalamic peptide regulates endothelial cell function and growth within the pituitary. VEGF secretion was also stimulated by interleukin-6 (IL-6) whereas basal, IL-6- and PACAP-stimulated secretion was inhibited by the synthetic glucocorticoid dexamethasone. The inhibitory action of dexamethasone was reversed by the glucocorticoid receptor antagonist RU486, suggesting that in FS cells functional glucocorticoid receptors mediate the inhibitory action of glucocorticoids on the VEGF secretion. The endocrine and auto-/paracrine control of VEGF production in pituitary FS cells by PACAP, IL-6 and glucocorticoids may play an important role both in angiogenesis and vascular permeability regulation within the pituitary under physiological and pathophysiological conditions.

Reduction of nitric oxide release from alveolar macrophages by a lipocortin peptide.

Nitric oxide (NO), produced by alveolar macrophages (AM) is used as a marker of respiratory tract inflammation. Lipocortin 1 (Lc-1) is an anti-inflammatory, glucocorticoid-inducible protein. The current aims were to determine whether (a) an Lc-1-derived peptide, Ac2-26, inhibited lipopolysaccharide (LPS)-induced NO release by primary AM in vitro and (b) the inhibitory action of dexamethasone was Lc-1-dependent. LPS treatment stimulated NO release from rat AM. Ac2-26 had little effect on unstimulated release, but suppressed LPS-stimulated release at concentrations > or =320 nM (320 nM, 10 +/- 3%; 3.2 microM, 15 +/- 3%; 32 microM, 27 +/- 4% NO inhibited, mean +/- SEM, n = 6). Inhibition by dexamethasone of NO release was unaffected by neutralizing anti-Lc-1 indicating that this action is Lc-1-independent in primary AM. Nevertheless inhibition of NO release by Ac2-26 (80 microM) was similar to that of 1 microM dexamethasone (Ac2-26, 40 +/- 6%; dexamethasone, 48 +/- 6% NO inhibited, mean +/- SEM, n = 6).

Dexamethasone inhibits the release of TSH from the rat anterior pituitary gland in vitro by mechanisms dependent on de novo protein synthesis and lipocortin 1

Glucocorticoids have been shown repeatedly to inhibit the secretion of TSH in experimental animals and in man but their site and mode of action are unknown. In the present study, we have used an in vitro model to examine the effects of dexamethasone on the resting and pharmacologically evoked secretion of TSH by the rat anterior pituitary gland, and to show how they are influenced by inhibitors of RNA/protein synthesis. In addition, we have investigated the potential role of lipocortin 1 (LC1), a protein shown previously to contribute to glucocorticoid action in several systems, as a mediator of the glucocorticoid-induced suppression of TSH release in our in vitro preparation. The significant (P < 0.01) increases in the release of immunoreactive (ir)TSH from rat anterior pituitary tissue initiated by submaximal concentrations of TRH (10 nmol/l), vasoactive intestinal polypeptide (VIP, 10 nmol/l) or the adenyl cyclase activator, forskolin (100 mumol/l) were reduced significantly (P < 0.05) by preincubation of the tissue with dexamethasone (0.1 mumol/l). In contrast, irTSH secretion evoked by a submaximal concentration of the L-Ca2+ channel opener BAY K8644 (10 mumol/l) was unaffected by the steroid, although readily antagonised (P < 0.01) by nifedipine (1-100 mumol/l). Inclusion of actinomycin D (1.78 mumol/l) or cycloheximide (0.8 mumol/l), inhibitors of RNA and protein synthesis respectively, in the medium effectively abrogated the inhibitory effects of dexamethasone (0.1 mumol/l) on the secretory responses to TRH (10 nmol/l), VIP (10 nmol/l) and forskolin (100 mumol/l). LC1 was readily detectable by Western blotting in protein extracts of freshly excised anterior pituitary tissue. A small proportion of the protein was found to be attached to the outer surface of the cells where it was retained by a Ca(2+)-dependent mechanism. Exposure of the tissue to dexamethasone (0.1 mumol/l) caused a pronounced increase in the amount of cellular LC1 attached to the outer surface of the cells and a concomitant decrease in the intracellular LC1 pool. Progesterone (0.1 mumol/l) and aldosterone (0.1 mumol/l) were also weakly active in this regard, but thyroxine and tri-iodothyronine (0.1 mumol/l) were not. Addition of an N-terminal LC1 fragment, LC1(1-188) (0.05-0.53 pmol/l) to the incubation medium reduced significantly (P < 0.01) the increases in irTSH release induced by TRH (10 nmol/l), VIP (10 nmol/l) and forskolin (100 mumol/l), but failed to influence (P < 0.05) those initiated by BAY K8644 (10 mumol/l). Furthermore, the inhibitory actions of dexamethasone (0.1 mumol/l) on the release of irTSH provoked by TRH (10 nmol/l), VIP (10 nmol/l) and forskolin (100 mumol/l) were substantially reversed (P < 0.01) by a specific monoclonal anti-LC1 antibody, while an isotype-matched control antibody was without effect. The results show clearly that dexamethasone, a semi-synthetic glucocorticoid, acts at the pituitary level to inhibit the neurochemically evoked release of irTSH. They also provide novel evidence that the inhibitory actions of the steroid are dependent upon de novo RNA/protein synthesis and that they involve an LC1 dependent mechanism.

Investigative Urology: Inhibitory Effect of Dexamethasone and Progesterone in Vitro on Proliferation of Human Renal Cell Carcinomas and Effects on Expression of Interleukin-6 or Interleukin-6 Receptor

Interleukin-6 (IL-6) has been suggested as an autocrine growth factor of human renal cell carcinomas. Since steroids are known to inhibit IL-6 gene expression, we investigated their effects on the growth of renal cell carcinoma. Dexamethasone inhibited proliferation of 2 of 4 renal cell carcinoma cell lines in a dose-dependent manner. In one of these 2 cell lines, IL-6 gene expression was also inhibited, but not in the other. The inhibitory effect of dexamethasone on cell proliferation was not reversed by the exogenous IL-6. In 1 of the 2 remaining cell lines, the inhibition of IL-6 gene expression was observed, although there was no inhibition of cell proliferation. Thus, inhibition of growth by dexamethasone did not correlate with an inhibitory action of dexamethasone on IL-6 mRNA expression. Progesterone inhibited the growth of 1 cell line without concomitant inhibition of IL-6 gene expression. Expression of IL-6 receptor mRNA was not altered. A dose-dependent increase in mRNA expression of gp130, the transducer of IL-6 signal, was induced by dexamethasone and progesterone in 2 and 1 of the 4 cell lines, respectively. These data suggest that, in some renal cell carcinomas, steroids may inhibit cell proliferation by a mechanism independent of their effects on mRNA expression of IL-6 and IL-6 receptors. Dexamethasone may be useful, not only for palliation of paraneoplastic syndrome caused by overproduction of IL-6, but also for inhibition of growth of renal cell carcinomas.

Inhibition of some aspects of acute inflammation of guinea-pig lung by intraperitoneal dexamethasone and mifepristone: demonstration of agonist activity of mifepristone in the guinea-pig.

We have determined the inhibitory activity of dexamethasone as an inhibitor of histamine-induced plasma protein extravasation (PPE) in guinea-pig lung and skin, and of lipopolysaccharide (LPS)-induced neutrophilia and platelet activating factor (PAF)-induced eosinophilia in guinea-pig lungs. Dexamethasone inhibited PAF-induced eosinophilia in guinea-pig lung (ED50 1.4 mg/kg i.p.). Higher doses of dexamethasone were required to inhibit LPS-induced neutrophilia (ED50 10.8 mg/kg i.p.). However, at doses up to 150 mg/kg i.p. dexamethasone did not inhibit histamine-induced plasma protein extravasation (PPE) in guinea-pig lung, but did inhibit PPE in guinea-pig skin. These preparations have previously been shown to be equally sensitive to inhibition by the beta 2-adrenoceptor agonist salmeterol. Dexamethasone inhibited PAF-induced eosinophilia (5 mg/kg) or LPS-induced neutrophilia (50 mg/kg) when given 3 h or 1 h prior to challenge. Inhibitory activity was lost when dexamethasone was administered 23 h prior to LPS or 1 h after PAF. The glucocorticoid antagonist mifepristone (1-100 mg/kg i.p.) caused dose-related inhibition of PAF-induced eosinophilia but not of LPS-induced neutrophilia. The highest dose of mifepristone used (100 mg/kg) did not reverse the inhibitory actions of dexamethasone (50 mg/kg) on LPS-induced neutrophilia. We suggest that the different inhibitory activity of dexamethasone in the preparations studied indicates differences in the sensitivity of the target cells involved to inhibition by dexamethasone. We also suggest that inhibition of PAF-induced eosinophilia by mifepristone reflects the partial agonist activity of this agent, demonstrated by others in different experimental systems.

Dexamethasone suppresses the release of prolactin from the rat anterior pituitary gland by lipocortin 1 dependent and independent mechanisms.

Glucocorticoids have been shown repeatedly to inhibit the release of prolactin (PRL) in the rat but their site and mode of action is unknown. In the present study, we used an in vitro model to examine the requirement for protein synthesis for dexamethasone to suppress the release of immunoreactive (ir)-PRL release from the rat pituitary gland. In addition we have performed a series of in vitro and in vivo experiments to investigate the potential role in this regard of lipocortin 1 (LC1), a protein shown previously not only to mediate aspects of the anti-inflammatory and anti-proliferative actions of the glucocorticoids but also to contribute to the regulatory actions of the steroids in the brain-neuroendocrine system. In vitro, the release of ir-PRL from rat anterior pituitary tissue initiated by submaximal concentrations of VIP (10 nM). TRH (10 nM) or the adenyl cyclase activator forskolin (100 microM) was reduced significantly (p < 0.01) by preincubation (2 h) of the tissue with dexamethasone (0.1 microM). By contrast, ir-PRL release evoked by a submaximal concentration of the L-Ca2+ channel opener BAY K8644 (10 microM) was unaffected by the steroid although readily antagonised (p < 0.01) by nifedipine (1-100 microM). Exposure of the pituitary tissue to dexamethasone (0.1 microM) also caused a pronounced and highly significant increase in de novo protein synthesis, as assessed by the incorporation of 14C-lysine into the tissue (p < 0.001). This response was reduced markedly by the inclusion of the RNA and protein synthesis inhibitors, actinomycin-D (0.5 micrograms/ml) or cycloheximide (1.0 micrograms/ml), in the incubation medium (p < 0.001), both of which also effectively abrogated (p < 0.01) the dexamethasone-induced inhibition of the release of ir-PRL evoked by TRH. VIP and forskolin. Lipocortin I was readily detectable by Western blotting in protein extracts of freshly excised anterior pituitary tissue: a small proportion of the protein was found to be attached to the outer surface of the cells where it was retained by a Ca(2+)-dependent mechanism. Exposure of the tissue in vitro to dexamethasone (0.1 microM) or corticosterone (0.1 microM) but not 17 beta-oestradiol (0.1 microM) caused a pronounced increase in the amount of LC1 attached to the outer surface of the cells and concomitant decrease in the LC1 content of the intracellular LC1 pool. Addition of an N-terminal LC1 fragment. LC11-188 (10 pg-10 ng/ml), to the incubation medium reduced significantly (p < 0.01) the increases in ir-PRL release induced in vitro by VIP (10 nM) and forskolin (100 microM). By contrast, at all concentrations tested. LC11-188 (10 pg-10 ng/ml) failed to influence (p < 0.05) the highly significant (p < 0.01) ir-PRL response to TRH (10 nM). Similarly, the inhibitory actions of dexamethasone (0.1 microM) on the release of ir-PRL induced by VIP (10 nM) or forskolin (100 microM) but not by TRH (10 nM) were substantially reversed (p < 0.01) by a specific monoclonal anti-LC1 antibody while an isotype-matched control antibody was without effect. In vivo, rats pretreated with either a polyclonal anti LC1 antiserum (anti-LC1 pAb, 1 ml/day s.c. for 2 days) or a corresponding volume of non-immune sheep serum (NSS) responded to stress (laparotomy under ether anaesthesia) with significant (p < 0.05) increases in the serum ir-PRL concentration. In the NSS-treated group, the ir-PRL response to stress was effectively inhibited by dexamethasone (100 micrograms/kg i.p.) which had no effect on the pre-stress serum ir-PRL concentration. By contrast, in rats pretreated with anti-LC1 pAb dexamethasone failed to block the stress-induced release of ir-PRL. The results show clearly that the inhibitory actions of dexamethasone on PRL release are dependent on de novo protein synthesis and provide novel evidence for the involvement of both LC1-dependent and LC1-independent mechanisms.

Immunoneutralization of lipocortin 1 reverses the acute inhibitory effects of dexamethasone on the hypothalamo-pituitary-adrenocortical responses to cytokines in the rat in vitro and in vivo.

Our recent studies suggest that lipocortin 1 (LC1), a potential mediator of the anti-inflammatory, antiproliferative and anti-fever actions of glucocorticoids in peripheral tissues, may also contribute to the powerful negative feedback actions of the steroids on the hypothalamo-pituitary-adrenal (HPA) axis. In the present study we have used (1) an in vitro model to examine the influence of a specific neutralizing monoclonal anti-LC1 antibody (anti-LC1 mAb) on the capacity of dexamethasone to suppress the cytokine-induced release of the 41-amino acid corticotropin-releasing factor (CRF-41) and arginine vasopressin (AVP) from the rat hypothalamus and (2) a passive immunization protocol to assess the contribution of LC1 to the inhibitory actions of dexamethasone on the HPA responses to immunological (i.p. injection of interleukin 1 beta, IL-1 beta) and surgical (laparotomy under ether anaesthesia) stress. In vitro, Il-1 alpha (0.2 ng/ml), IL-1 beta (0.5 ng/ml), IL-6 (10 ng/ml) and IL-8 (1 ng/ml) each caused significant increases in the release of immunoreactive (ir)-CRF-41 and ir-AVP from hypothalami removed from rats adrenalectomized 10-12 days before autopsy; these responses were readily inhibited by preincubation of the tissue with dexamethasone (10(-7) M). The inhibitory actions of the steroid were attenuated and, in many instances, abolished by inclusion in the medium of a monoclonal anti-LC1 antibody (LC1 mAb, diluted 1:15,000); an isotype-matched control antibody (antispectrin alpha+beta, diluted 1:15,000) was ineffective in this regard. IL-1 alpha (0.2 ng/ml), IL-1 beta (0.5 ng/ml) and IL-6 (10 ng/ml) also initiated similar increases in the release of CRF-41 and AVP from hypothalami from intact rats which were effectively blocked by dexamethasone (10(-7) M). However, although the inhibitory actions of the steroid on the pharmacologically evoked release of CRF-41 were specifically overcome by anti-LC1 mAb (diluted 1:15,000), the steroid blockade of AVP release was not. In vivo, rats pretreated with either a polyclonal anti-LC1 antibody (anti-LC1 pAb, 1 ml/day s.c. for 2 days) or a corresponding volume of a nonimmune sheep serum (NSS) responded to immunological (IL-1 beta, 3 micrograms/kg i.p.) or surgical (laparotomy under ether anaesthesia) trauma with significant increases in the serum ACTH and corticosterone concentrations. In the NSS-treated groups, dexamethasone (100 micrograms/kg), which had no effect on the prestress concentrations of ACTH and corticosterone in the blood, completely prevented the HPA responses to both IL-1 beta and laparotomy.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition by dexamethasone of retinoic acid-induced enhancement of leukotriene C4 synthesis in rat basophilic leukemia-1 cells.

We investigated inhibitory actions of dexamethasone (DEX) on retinoic acid (RA)-induced enhancement of leukotriene C4 (LTC4) synthesis in rat basophilic leukemia-1 (RBL-1) cells. Cultured cells were preincubated with RA for 16 h with or without DEX, and generation of LTC4 was measured by high performance liquid chromatography in cell-free and intact cell systems. RA (0.1 microgram/ml) significantly potentiated calcium ionophore-stimulated production of LTC4 synthesis. DEX inhibited the RA-induced enhancement of LTC4 synthesis by up to approximately 95% in intact cells when stimulated with calcium ionophore. RA-induced LTC4 synthase activity, which was determined by enzyme assay, was also inhibited by DEX by 65% in a cell-free system. This discrepancy of inhibition between the intact and cell-free systems was due to a partial inhibition of phospholipase A2 activity by DEX in the intact cells. These results indicate that the production of LTC4 is predominantly regulated at a level of LTC4 synthase. The induction of new LTC4 synthase activity by RA and inhibition of the RA-induced activity by DEX are important regulatory mechanisms of LTC4 synthesis.

Cyclic adenosine monophosphate prevents the glucocorticoid-mediated inhibition of insulin gene expression in rodent islet cells.

Dexamethasone negatively regulates insulin gene expression in HIT-15 cells. In vivo, however, an excess of glucocorticoids results in an increase in insulin biosynthesis and peripheral hyperinsulinemia. To resolve this contradiction, we have studied the effects of dexamethasone in primary rat islet cells. We show here that dexamethasone decreases insulin mRNA levels in single islet cells, as in HIT-15 cells, but does not affect these levels in reaggregated islet cells and increases them in intact islets of Langerhans. Because cAMP is an important regulator of insulin gene expression and intracellular cAMP content may be decreased in single beta cells, we investigated whether cAMP could prevent the inhibitory effect of dexamethasone on insulin mRNA levels. In the presence of cAMP analogues, the inhibitory action of dexamethasone was not only prevented, but insulin mRNA increased to levels comparable to those observed when cAMP analogues were used alone. We conclude that the insulin gene is negatively regulated by dexamethasone in single islet cells, but that other factors such as cAMP prevent this effect when the native environment of islet cells is preserved. Our results indicate that insulin gene regulation is influenced by cell to cell contacts within the islet, and that intracellular cAMP levels might be influential in this regulation.

Posttranscriptional regulation of surfactant protein-A messenger RNA in human fetal lung in vitro by glucocorticoids.

Surfactant protein-A (SP-A), the major pulmonary surfactant-associated protein, is a developmentally and hormonally regulated sialoglycoprotein of about 35,000 mol wt. In previous studies we observed that dexamethasone has dose-dependent biphasic effects on the levels of SP-A and its mRNA in human fetal lung in vitro. At concentrations of 10(-10)-10(-9) M, dexamethasone increased the levels of SP-A and its mRNA over those of control tissues, whereas at concentrations greater than or equal to 10(-8) M, the steroid was markedly inhibitory. Our findings suggest that the inhibitory action of dexamethasone (greater than 10(-8) M) on SP-A mRNA levels was mediated by an effect to reduce SP-A mRNA stability, since the steroid caused a dose-dependent increase in the rate of transcription; however, an effect to increase transcription with premature termination leading to instability of mRNA transcripts could not be ruled out. In the present investigation we have studied in detail the mechanisms underlying the biphasic effects of glucocorticoids on SP-A mRNA levels in human fetal lung tissues in vitro. Our findings indicate that dexamethasone (10(-7) M) has no adverse effect on the elongation of nascent mRNA transcripts throughout the SP-A gene; elongation of SP-A mRNA transcripts in dexamethasone-treated tissue explants was similar to that observed in tissues incubated in control medium or medium containing (Bu)2cAMP. Therefore, premature termination of SP-A mRNA transcription leading to the instability of SP-A mRNA can be ruled out. On the other hand, we found that dexamethasone (10(-7) M) had a pronounced effect to reduce the apparent half-life of SP-A mRNA; in control explants maintained in the presence of actinomycin-D to block gene transcription, the SP-A mRNA half-life was estimated to be 11.4 h, whereas in tissues also treated with dexamethasone, the SP-A mRNA half-life was reduced by more than 60% to 5.0 h. Dexamethasone also was found to have dose-dependent effects on the degradation of SP-A mRNA. After 12 h of incubation in the presence of actinomycin-D and dexamethasone at 10(-9) and 10(-7) M, the levels of SP-A mRNA were reduced by 50% and 80%, respectively, compared to those in tissue incubated with actinomycin-D alone. The inhibitory effects of glucocorticoids on SP-A mRNA levels were completely reversible and were blocked by the glucocorticoid antagonist RU486.(ABSTRACT TRUNCATED AT 400 WORDS)