Inhibition of prostaglandin biosynthesis by corticosteroids requires RNA and protein synthesis

Adrenal Insufficiency in the Intensive Care Setting

In the intensive care setting, the question of adrenal insufficiency arises most frequently in patients whose endogenous adrenal function may be suppressed by pre ceding glucocorticoid therapy or in patients with the acquired immunodeficiency syndrome. Less often the question arises in patients whose adrenal tissue may have been destroyed by autoimmune disease, tuber culosis, meningococcal or other infection, hemorrhage, or replacement by malignancy, or in patients whose adrenal function has been suppressed by certain drugs. Measurements of plasma adrenocorticotrophic hor mone (ACTH), cortisol, aldosterone, and renin levels and the response of cortisol and aldosterone to exoge nously administered ACTH form the basis for clinically evaluating the adequacy of a patient's adrenal function. The naturally occurring glucocorticoid, hydrocortisone, remains the cornerstone of adrenal replacement therapy along with appropriate fluid and electrolyte administra tion. In rare instances the addition of a mineralocor ticoid is necessary. A brief review of the use of mega- dose glucocorticoids in the treatment of sepsis, shock, and the adult respiratory distress syndrome is included.

TNF and PGE(2) in human monocyte-derived macrophages infected with Chlamydia trachomatis

In this study levels of prostaglandin E₂ (PGE₂), tumour necrosis factor (TNF) and interleukin-1 (IL-1) alpha in medium from monocyte derived macrophages (MdM) infected with Chlamydia trachomatis (L₂/434/Bu or K biovars). TNF and PGE₂ were found in both cases while IL-1 alpha was not detected. Both TNF and PGE₂ levels were higher in the medium of the MdM infected with K biovars. TNF reached maximum levels 24 h postinfection, and then declined, while PGE₂ levels increased continuously during the infection time up to 96 h post-infection. Addition of dexamethasone inhibited production of TNF and PGE₂. Inhibition of PGE₂ production by indomethacin resulted in increased production of TNF, while addition of PGE₂ caused partial inhibition of TNF production from infected MdM.

Regulation of pulmonary arachidonic acid metabolism by anti-inflammatory steroids

Enzymes in cells from many tissues including the lung metabolize arachidonic acid to a variety of highly active local hormones such as prostaglandins and 'slow-reacting substances'. Many of these play a part in the inflammatory response which follows injury or trauma or, in the case of slow-reacting substance, asthmatic bronchoconstriction. Both non-steroidal and steroidal anti-inflammatory drugs inhibit the formation of some or all of these products. The non-steroidal drugs block prostaglandin formation but not the formation of products such as slow-reacting substances. The steroids block the formation of all products. Their mechanism of action, investigated in the guinea-pig perfused lung, involved inhibition of arachidonic acid liberation, probably by suppression of phospholipase activity. To achieve this steroids must first bind to receptors in lung tissue and initiate de novo RNA and protein synthesis. This culminates in the synthesis or secretion by some cells in the lung of a polypeptide of mol.wt. 10 000-15 000 with potent anti-phospholipase properties. The generation of this factor could partly explain why steroids are so effective in the treatment of many types of inflammatory disease, and in particular why they are so efficacious against asthma.

Topical glucocorticoids and the skin--mechanisms of action: an update

The topical glucocorticoids (GCs) represent the treatment of choice for many types of inflammatory dermatoses. Despite the extensive use of this class of drugs as first line therapy the mechanism of their action is uncertain. It is clear that the multiplicity of actions of the topical GCs is an important facet of their scope in the treatment of dermal disorders. The aim of this update is to review past and current theories regarding how these agents might work. Current understanding of the molecular mechanisms of GC action has advanced significantly over the past decade with the realisation that multiple systems are responsible for transduction of GC effects at a molecular level. The two primary modes of action are via interaction directly with DNA or indirectly through modulation of specific transcription factors: the endpoint in both cases being modulation of specific protein synthesis. Both of these mechanisms will be discussed. In particular this review will concentrate on the possibility that a GC-inducible protein, termed lipocortin 1, may have a significant role to play in the anti-inflammatory actions of these drugs. Additionally it has become apparent that several inflammatory enzymes induced in inflammation are sites of inhibitory action of the GCs, and the possibility that this occurs in the skin will be discussed paying particular attention to the inducible phospholipase A2, nitric oxide synthase and cyclooxygenase systems.

Effect of dexamethasone on the peptic activity of gastric lumen and mucosa

Dexamethasone (9 alpha-fluoro-16 alpha methyl-11 beta,17 alpha,21-trihydroxy-1,4-pregnadiene-3,20-dione-21-phosphate), a synthetic glucocorticoid, has a dual role on pepsinogen content of the gastric lumen and mucosa as measured by its peptic activity. Following stimulation the luminal peptic activity gradually decreases after 6 hr, then returns to basal levels at 18 hr and by 24 hr is inhibited by 50%. The luminal peptic activity induced by the secretory compound mercaptomethylimidazole (MMI) is also decreased. Dexamethasone effect on both basal and MMI-induced peptic activity can be reproduced by cycloheximide or puromycin, translational blockers of protein synthesis. This drug also has an independent time and dose-dependent inhibitory effect on gastric mucosal peptic activity which does not correlate with increased peptic activity of the lumen. Dexamethasone appears to be more effective than hydrocortisone and corticosterone in inhibiting the basal peptic activity of both lumen and mucosa. The inhibitory effect of this drug on tissue peptic activity is not mediated through induction of any inhibitory protein as evidenced by the insensitivity of the effect to actinomycin D. Studies on [14C]phenylalanine incorporation into gastric protein indicate that the effect of dexamethasone on tissue pepsinogen content is not due to a generalized block of protein synthesis.

Effects of lipocortin 1 and dexamethasone on the secretion of corticotrophin-releasing factors in the rat: in vitro and in vivo studies

Lipocortin 1 (LC1: also called annexin 1) was first described as a putative second messenger protein for the anti-inflammatory steroids in peripheral tissues. In the present study, in vitro and in vivo methods were used to examine its potential role within the hypothalamus as a mediator of the regulatory actions of the glucocorticoids on the hypothalamo-pituitary-adrenocortical axis of the rat. In the in vitro studies, the effects of human recombinant LC1 (hu-r-LC1) on the concomitant release of the two major corticotrophin-releasing factors (CRF-41 and arginine vasopressin, AVP) from isolated hypothalami removed from chronically adrenalectomized rats were compared with those of dexamethasone in the presence and absence of appropriate secretagogues, namely phospholipase A2 (PLA2), interleukin-6 (IL-6) and a non-specific depolarizing agent, K+ (56 mM). The spontaneous release of CRF-41 in vitro was unaffected by either hu-r-LC1 (5 to 100 ng/ml) or dexamethasone (1 microM). Both compounds however reduced the release of the neuropeptide evoked by IL-6 (5 ng/ml) but failed to modify the secretory responses to PLA2 (25 U/ml) or K+ (56 mM). Dexamethasone (1 microM) had no effect on the basal release of AVP but effectively blocked the secretion of the peptide induced by either IL-6 (10 ng/ml) or PLA2 (25 U/ml). In complete contrast, hu-r-LC1 (5 to 100 ng/ml) stimulated the release of AVP and potentiated the secretory responses to IL-6 (10 ng/ml) and PLA2 (25 U/ml) but not to K+ (56 mM). The hypothalamic responses to PLA2 stimulation (25 U/ml) were associated with significant (P < 0.01) increases in prostaglandin E2 release which, in some instances, were potentiated by hu-r-LC1 (5 to 20 ng/ml). In vivo, administration of histamine (0.6 mg/100 g body wt, ip) produced significant (P < 0.01) increases in the serum corticosterone concentration and in the hypothalamic LC1 content. Neither hu-r-LC1 (0.6 to 1.2 micrograms) nor a polyclonal anti-LC1 antibody (3 microliters, diluted 1:200), injected intracerebroventricularly (icv), influenced either the resting serum corticosterone concentration or the hypersecretion of the steroid evoked by histamine stress. A lower dose of the recombinant protein (0.3 micrograms icv) also failed to alter basal corticosterone release but, in contrast to the higher doses, potentiated the pituitary-adrenocortical responses to histamine. The results suggest that LC1 may contribute to some aspects of peptide release in the hypothalamus but that its actions are not necessarily related to those of the glucocorticoids.

Effect of insulin on the decreased beta-adrenergic responses of duodenum and atrium isolated from streptozotocin diabetic rats

1. Decreased beta-adrenergic responses have been reported in both gastro-intestinal tract and atrium of experimentally-induced diabetic rats. The present study was undertaken to investigate in vitro effects of insulin on decreased beta-adrenergic responses of the duodenum and atrium from streptozotocin-diabetic rats. 2. Insulin incubation (16.67 micrograms/ml) in bathing medium for 5 hr enhanced the decreased beta-adrenergic responses in the diabetic rat duodenum, but not those in the diabetic atrium. Incubation of bovine insulin with anti-bovine insulin antibody in the test-tube inhibited the improving effect of insulin on the decreased beta-adrenergic responses of diabetic rat duodenum. 3. In vitro treatment with the same dose of bovine insulin in bathing medium caused a decrease in the beta-adrenergic responses of the atria from both non-diabetic and diabetic rats. Anti-bovine insulin antibody also abolished the inhibitory effect of insulin on the rat atria. 4. These results strongly suggest that the experimental diabetes affects beta-adrenergic responsiveness of the rat gastro-intestinal tract through a different mechanism from that of the rat myocardium.

Effects of catecholamines on eicosanoid synthesis with special reference to prostanoid/leukotriene ratio

Catecholamines (adrenaline, dopamine, and noradrenaline) stimulate prostanoid synthesis by acting as "cosubstrates." On the other hand, many inhibitors of leukotriene synthesis, such as nordihydroguaiaretic acid and caffeic acid, have a catecholic structure. Catecholamines have opposite effects on prostanoid and leukotriene synthesis in human polymorphonuclear leukocytes and whole blood. Basic phenols (catechol, hydroquinone, and phenol) also increase the prostanoid/leukotriene ratio in polymorphonuclear leukocytes. These actions correlate to their antioxidant capacities and oxidation potentials, and they are not mediated via adrenergic receptors. There is only limited knowledge about the effects of natural catecholamines on the prostanoid/leukotriene ratio in vitro and in vivo. Indirect data suggest that catecholamines could increase prostanoid production in physiological or pathological situations, such as heavy physical exercise, myocardial infarction, and surgical stress. This interaction may also be of clinical importance in asthma, gastric ulcer, and psoriasis, where decreased prostanoid/leukotriene ratios have been reported.

Lack of prostaglandin effect on sodium balance and hyperreninemia in adrenalectomized rats

Glucocorticoids are known inhibitors of prostaglandin production. Prostaglandin E2 (PGE2) and prostacyclin (PGI2) are promoters of natriuresis and renin release. Excessive prostaglandin production, therefore, might contribute to the altered sodium balance and renin release observed in primary adrenal insufficiency. To test this hypothesis, sodium balance and prostaglandin production were measured in adrenalectomized rats and in animals receiving prostaglandin inhibitors or replacement dexamethasone. Compared to sham-operated controls, adrenalectomized rats had decreased two-day sodium balance and elevated plasma renin concentration (PRC), renal PGE2 production, and renal 6-ketoprostaglandin F1 alpha (6kPGF1 alpha, the nonenzymatic metabolite of PGI2); however, no appreciable change in aortic 6kPGF1 alpha production was observed. Dexamethasone given to adrenalectomized rats normalized PRC but had no effect on sodium balance or prostaglandin production. Likewise, prostaglandin inhibitors did not alter the sodium balance or decrease the PRC post adrenalectomy. These data confirm renal prostaglandin production is increased in adrenalectomized rats, but suggest that the elevation is not due directly to glucocorticoid deficiency. Further, PRC levels in adrenal insufficiency do not appear to be prostaglandin mediated. In conclusion, excessive renal prostaglandin production does not contribute to altered sodium balance or increased PRC in adrenalectomized rats.

Biphasic regulation by dexamethasone of IL-1- and LPS-stimulated endothelial prostacyclin production

Body reaction to injury comprises two major pathways: the immune response, predominantly mediated by IL-1 and other cytokines, and neuroendocrine mechanisms, resulting in an increased glucocorticoid production. Each has distinct effects on prostaglandin (PG) production, which may in turn mediate both systemic and local inflammatory responses. The interactions, if any, between the two systems on PG synthesis have not been studied. Bovine aortic endothelial cell cultures were used and prostacyclin (PGI2) production was monitored. Cells were treated with dexamethasone (Dex) 10(-6) M and IL-1 10-30 U/ml in one experiment, and lipopolysaccharide (LPS, 0.1-1.0 micrograms/ml) in another experiment, separately or in combination, for either 2 or 24 + 2 h. While Dex was without effect, IL-1 and LPS stimulated PGI2 in a concentration- and time-dependent manner. Short exposure to Dex (2 h) enhanced the stimulation by IL-1 and LPS. On the contrary, more prolonged exposure (24 + 2 h) reversed the effects of IL-1 and LPS, resulting in PGI2 levels below the baseline. A biphasic regulation by Dex was also observed with increasing concentrations of LPS. Dex was actually ineffective by itself, but it enhanced PGI2 production in combination with lower concentrations of LPS, while abolishing the influence of higher concentrations of this agonist. The data suggest that Dex may initially stimulate phospholipase A2 (PLA2) activity, while inhibiting it later. This biphasic behavior may be attributed to different concentrations of a PLA2-modulating protein, possibly lipocortin, that accumulate during exposure to Dex.

Corticosteroids inhibit the delivery of short-term activational pulses of phorbol ester and calcium ionophore to human peripheral T cells

Although there is evidence that corticosteroids inhibit receptor-ligand-induced phospholipid hydrolysis, the immunosuppressive effects of these agents downstream of protein kinase C (PK-C) activation and cytosolic Ca2+ mobilization is unclear. Previous studies indicated that T cell proliferative activation could be achieved with simultaneous short-term (e.g., 15-120 min) exposure to agents activating PK-C and elevating cytosolic Ca2+. In the studies reported here, similar procedures were utilized for determining whether corticosteroids alter T cell activation signals downstream of second messenger events. Dexamethasone interfered with T cell activation induced by short-term exposure to phorbol 12,13-dibutyrate (PDBu) and the calcium ionophore, ionomycin. The inhibitory effect was evident with as little as 15 min of exposure to dexamethasone and T cell activating agents, making mechanisms involving de novo protein synthesis unlikely. Dexamethasone's effects in this system were blocked by the steroid receptor antagonist RU-486, indicating that the inhibition was mediated through the glucocorticoid receptor. The inclusion of recombinant interleukin-2 (IL-2) only partially overcame the dexamethasone inhibitory effect. Long-term (i.e., 48 hr) direct stimulation of PK-C with either PDBu or the non-tumor-promoting PK-C activator, bryostatin 1, also substantially overcame dexamethasone's effects, resulting in a recovery of IL-2 production and significant restoration of the T-cell proliferative response. These observations suggest that treatment with a PK-C-activating agent such as bryostatin 1 could reduce glucocorticosteroid-induced immunosuppression.

Biphasic regulation by dexamethasone of IL-1- and LPS-stimulated endothelial prostacyclin production

Body reaction to injury comprises two major pathways: the immune response is predominantly mediated by IL-1 and other cytokines, and neuroendocrine mechanisms, resulting in increased glucocorticoid production. Each has distinct effects on prostaglandin (PG) production, which may in turn mediate both systemic and local inflammatory responses. The interactions, if any, between the two systems on PG synthesis have not been studied. Bovine aortic endothelial cell cultures were used and prostacyclin (PGI2) production was monitored. Cells were treated with dexamethasone (Dex) 10(-6) M and IL-1 10-30 U/ml in one experiment, and lipopolysaccharide (LPS, 0.1-1.0 microgram/ml) in another experiment, separately or in combination, for either 2 or 24 + 2 h. While Dex was without effect, IL-1 and LPS stimulated PGI2 in a concentration and time dependent manner. Short exposure to Dex (2 h) enhanced the stimulation by IL-1 and LPS. On the contrary, more prolonged exposure (24 + 2 h) reversed the effects of IL-1 and LPS, resulting in PGI2 levels below baseline. A biphasic regulation by Dex was also observed with increasing concentrations of LPS. Dex was actually ineffective by itself, but it enhanced PGI2 production in combination with lower concentrations of LPS, while abolishing the influence of higher concentrations of this agonist. The data suggest that Dex may initially stimulate phospholipase A2 (PLA2) activity, while inhibiting it later. This biphasic behavior may be attributed to different concentrations of a PLA2-modulating protein, possibly lipocortin, that accumulate during exposure to Dex.

Glucocorticoid-mediated alterations in fluidity of rabbit cardiac muscle microvessel endothelial cell membranes: influences on eicosanoid release

Experiments were conducted to determine effects of the synthetic glucocorticoid, dexamethasone, on the lipid fluidity of cultured rabbit cardiac muscle microvessel endothelial cells and the possible role(s) for altered fluidity in the steroid inhibition of cellular eicosanoid production. Following a sixteen hour exposure to 10(-7) M dexamethasone, membranes prepared from treated cells exhibited a decreased fluidity compared to their control counterparts, as assessed by steady-state fluorescence polarization techniques using 1,6-diphenyl-1,3,5-hexatriene (DPH). Examination of the effects of temperature on the anisotropy values of DPH using Arrhenius plots revealed consistent differences in the steroid treated cells over the entire temperature range (40-5 degrees C). These dexamethasone-dependent fluidity changes were associated with increases in the cholesterol/phospholipid ratio of membrane lipids. Restoration of membrane fluidity to control values with the fluidizing agent, 2-(2-methoxyethoxy)ethyl-8-(cis- 2-n-octylcyclopropyl)octanoate (A2C), partially reversed dexamethasone induced inhibition of A23187-stimulated eicosanoid release. These observations suggest that at least part of dexamethasone's inhibitory actions on eicosanoid generation in microvessel endothelial cells are mediated by alterations in membrane composition and fluidity.

Glucocorticoids increase the synthesis of immunoglobulin E by interleukin 4-stimulated human lymphocytes

This study indicates that hydrocortisone (HC) markedly increases the synthesis of immunoglobulin E (IgE) by interleukin 4 (IL-4)-stimulated human lymphocytes. The effect is glucocorticoid specific and is obtained with low concentrations of HC (0.1-10 microM). In both the early and the late phase of the IL-4-induced response HC exerts its effects which are respectively IL-4 dependent and IL-4 independent. The IgE potentiation cannot be explained by the inhibition of interferon-gamma (IFN-gamma) production since it is observed in the absence of endogenous secretion of IFN-gamma. HC inhibits the production of IgE-binding factors (soluble CD23) and the expression of the low-affinity receptor for IgE, also known as the (Fc epsilon RII) CD23 antigen; however, the residual expression of Fc epsilon RII by IL-4- and HC-treated peripheral blood mononuclear cells (PBMCs) is important since the IgE response of these cells is markedly inhibited by anti-CD23 monoclonal antibody. HC acts mainly by amplifying the cellular interactions between monocytes and lymphocytes; indeed, HC has no effect on monocyte-depleted PBMCs, and moreover, monocytes cannot be replaced by soluble factors. Most importantly, T cells are not required for the induction of IgE synthesis by costimulation with IL-4 and HC. However, the IgE response of rigorously T cell-depleted PBMCs may be further increased by the addition of T cells. Further analysis of the permissive effect of HC on the synthesis of IgE by T cell-depleted PBMCs suggests that HC acts in synergy with IL-4 to trigger the activation and the differentiation of B cells into IgE-producing cells.

The presence of autoantibody to recombinant lipocortin-I in patients with psoriasis and psoriatic arthritis

Corticosteroids may mediate some of their anti-inflammatory effects via induction of a specific 38 kDa protein, lipocortin-I. Anti-lipocortin-I antibodies (ALA) were measured by enzyme-linked immunosorbent assay (ELISA) in 23 patients with plaque-type psoriasis alone (NAP), in 21 patients with psoriasis and arthritis (PA), and in 67 healthy controls. Only two of 23 NAP patients had elevated ALA, whereas six of 21 PA patients had raised levels of ALA (P = 0.2). Sero-negative polyarthritis was the most common pattern of joint disease in those PA patients with elevated ALA (4/6). ALA levels did not correlate with the extent or severity of cutaneous involvement, and are unlikely to be involved in the pathogenesis of cutaneous psoriasis.

Brain protection: physiological and pharmacological considerations. Part II: The pharmacology of brain protection

Neuroprotective agents may exert their effect by reducing cerebral oxygen demand (CMRO2), increasing cerebral oxygen delivery, or by altering ongoing pathological processes. Barbiturates provide neuroprotection by reducing the CMRO2 necessary for synaptic transmission while leaving the component necessary for cellular metabolism intact. Isoflurane may exert a neuroprotective effect by a similar mechanism but its efficacy is likely less than that of barbiturates due to adverse effects on cerebral blood flow. Lidocaine reduces CMRO2 by affecting both cellular metabolic processes and synaptic transmission and thus resembles hypothermia in its mechanism of action. Benzodiazepines reduce CMRO2 by reducing synaptic transmission and their use as neuroprotectants produces less haemodynamic compromise than barbiturates. The mechanism of protection by calcium entry blocking agents appears to be due to improved blood flow as opposed to altering abnormal Ca++ fluxes. In contrast, agents such as ketamine and MK-801 may prevent abnormal Ca++ fluxes through their competitive interaction with N-methyl-D-aspartate receptors. Phenytoin prevents K(+)-mediated ischaemic events from progressing. Agents worthy of further investigation include corticosteroids, free radical scavengers, prostaglandin inhibitors and iron chelators.

Glucocorticoid-induced reduction of prostanoid synthesis in TPA-differentiated U937 cells is mainly due to a reduced cyclooxygenase activity

The molecular mechanism of the glucocorticoid-induced inhibition of prostanoid synthesis was investigated in human monoblastoid U937 tumor cells and phorbol ester (TPA)-differentiated U937 cells. Prostanoid synthesis was inhibited in TPA-differentiated U937 cells by glucocorticoids such as dexamethasone and prednisolone, whereas aldosterone and progesterone showed no inhibitory effect. None of these methods had any influence on prostanoid secretion of undifferentiated U937 cells. Receptor binding studies revealed the presence of glucocorticoid receptors in both undifferentiated and TPA-differentiated U937 cells (Kp approximately 5 x 10(-9)M), however, the number of receptors per cell was increased 10-fold in TPA-differentiated U937 cells. Expression of lipocortin I and II as measured by Western blot analysis was not affected by dexamethasone. In TPA-differentiated cells, dexamethasone decreased the activities of two enzymes essential for prostanoid synthesis, cyclooxygenase and phospholipase A2, by 60-70% and 30%, respectively. Cells pretreated with the translation inhibitor cyclohexmide and dexamethasone showed similar cyclooxygenase and phospholipase A2 activities as cells treated with cycloheximide alone. Western blot analysis demonstrated that the significantly decreased cyclooxygenase activity correlated with an inhibited protein synthesis. In this human macrophage-like model glucocorticoids thus interfere at least at two levels with prostanoid synthesis by inhibiting the activities of phospholipase A2 as well as cyclooxygenase.

Tumor necrosis factor alpha and prostaglandin E2 production by human monocyte-derived macrophages infected with spotted fever group rickettsiae

Infection of macrophages by intracellular parasites might modulate production of tumor necrosis factor (TNF) and prostaglandin E2 (PGE2), which, in turn, might have a profound effect on the outcome of the infection in vivo. In this study we examined in an in vitro system, the rickettsial yield in human monocyte-derived macrophages (MdM) and the PGE2 and TNF production by MdM infected with Rickettsia conorii RC, Casablanca strain) or Israeli spotted fever (ISF, G-212 strain). TNF and PGE2 were determined in the media of MdM infected with RC or ISF. TNF reached maximum levels 24 h post-infection and then declined, while PGE2 levels increased continuously during the infection up to 96 h post-infection. Addition of dexamethasone inhibited both TNF and PGE2 production and enhanced rickettsial yield in MdM. Inhibition of PGE2 production by indomethacin resulted in increased production of TNF from rickettsial-infected MdM, while addition of PGE2 caused partial inhibition of TNF production from infected MdM.

Proteinaceous inhibitors of phospholipase A2 purified from inflammatory sites in rats

We have purified two phospholipase A2 inhibitory proteins (37 and 33 kDa) from peritoneal fluid of dexamethasone-treated rats. The extracellular phospholipase A2 found in inflammatory sites differed from the exocrine phospholipase A2 in susceptibility to these endogenous inhibitors; both proteins inhibited the activity of the extracellular phospholipase A2 purified from sites of inflammation but did not affect appreciably the activity of either porcine pancreatic or Naja naja venom phospholipase A2. The amino acid sequence of the NH2-terminal portion of the purified proteins did not resemble that of lipocortins so far reported, but it was almost identical to that of parts of human or mouse complement component C3. These findings may indicate that degraded products of C3 are involved in the regulation of activity of a class of mammalian phospholipase A2.

Biology of phospholipase inhibitory proteins

Our present results showed that calpactins might be not the proteins whose synthesis is modulated by glucocorticoids, and suggest that there may be another type of PLA2 inhibitory protein which directly interact with PLA2 and whose synthesis is induced by glucocorticoids. Further characterization and isolation of this protein will provide the most concrete evidence in this aspect.

The role of platelets in blood-aqueous barrier breakdown induced by anterior chamber paracentesis in the rabbit

Anterior chamber paracentesis of the rabbit eye causes disruption of the blood-aqueous barrier, which is characterized by a rapid increase in the albumin and total protein content of the aqueous humor. Prostaglandins appear to be implicated as major mediators in this reaction, since a cyclooxygenase inhibitor, indomethacin, very efficiently prevents protein leakage. When paracentesis was performed in platelet-depleted rabbits (either by transfusion or by treatment with an antiplatelet plasma), the protein content in the aqueous humor did not rise to values observed in normal animals. These data suggest that platelets play some role in the response to paracentesis, a fact in accordance with histological results. In contrast to cyclooxygenase inhibitors, dexamethasone inhibits neither the blood-aqueous barrier breakdown nor prostanoid release from platelets. These data also indirectly indicate the possible role of platelets in triggering the paracentesis reaction in the rabbit.

Differential effect of dexamethasone on the regulation of phospholipase A2 and prostanoid synthesis in undifferentiated and phorbolester-differentiated U937 cells

The human undifferentiated histiocytic cell-line U937 can be induced to differentiate by incubation with 12-0-tetradecanoylphorbol-13-acetate (TPA) into macrophage-like cells. Dexamethasone reduced the prostaglandin production in TPA-differentiated U937 cells dose dependently, whereas undifferentiated U937 cells were dexamethasone insensitive. Concomitantly phospholipase A2, the enzyme liberating the prostaglandin precursor arachidonic acid, was inhibited by dexamethasone in TPA-differentiated but not in undifferentiated U937 cells. The activity of lysophosphatide acyltransferase, the key enzyme of fatty acid reacylation into phospholipids, remained unchanged both in undifferentiated and TPA-differentiated U937 cells. The data suggest that responsiveness to glucocorticoid-dependent regulation of prostanoid synthesis is acquired by cells of the monocyte-macrophage lineage late in differentiation.

Effect of glucocorticoid on liver regeneration after partial hepatectomy in the rat

The increase in activities of hepatic thymidylate synthetase (EC 2.1.1.45) and thymidine kinase (EC 2.7.1.21), which catalyse the formation of thymidylate through the de novo and salvage pathways, respectively, were significantly suppressed during liver regeneration in rats which were given glucocorticoids (hydrocortisone and dexamethasone) or indomethacin. These drugs also prevented the augment of hepatic DNA content in 24 h regenerating liver.

Effect of methylprednisolone on nitrogen dioxide (NO2)-induced pulmonary edema in guinea pigs

The treatment of nitrogen dioxide (NO2)-induced lung edema is controversial. In addition, mechanisms and patterns of interstitial edema formation in this form of increased permeability edema are unclear. To ascertain if methylprednisolone (MP) is effective in the therapy of NO2-induced edema, we exposed 108 unaesthetized guinea pigs, in groups of 12, to 277-448 ppm.hr NO2: in 60, we administered MP just before, and in 48 immediately after exposure. In each group, half the animals were randomly assigned to receive 30 mg/kg MP ip, and the other half saline. Mortality rates and lung water with wet weight/dry weight (W/D) ratios were calculated. Alveolar edema, periarterial interstitial edema, and NO2-induced bronchiolitis were graded semiquantitatively by light microscopy from freeze-substituted middle (ML) and lower lobes (LL). We found NO2 produced an exposure-dependent increase in lung water (R = 0.70, p less than 0.01). Treatment with MP preexposure produced a fourfold reduction mortality, and and a significant fall in W/D ratios and in alveolar and interstitial edema. No difference in the degree of acute bronchiolitis was found between treated and untreated animals, although ML had significantly more inflammation than LL. Treatment with MP immediately after NO2 was ineffective since mortality rates, W/D ratios, and alveolar and interstitial edema were not lower in the treated animals; there was significantly more intestitial edema in the middle lobes of the latter. Both LL and ML had equally abundant alveolar edema, but LL had significantly more interstitial edema, supporting our previous findings that in NO2-induced edema interstitial fluid accumulation follows alveolar flooding, with interlobar discrepancies probably due to differences in lung volume or in ventilation.

Steroid-induced enhancement of functional recovery of postischemic, reperfused myocardium in conscious dogs

The effects of methylprednisolone sodium succinate (20 mg/kg, intravenously administered) on the time course of functional recovery of myocardium following a 15-minute coronary artery occlusion period and subsequent 5 hour reperfusion period were studied in chronically instrumented, conscious dogs. In comparison to a control group, animals receiving methylprednisolone 90 minutes prior to coronary occlusion demonstrated less depression of regional segment shortening following 15 minutes of reperfusion (52 +/- 13% vs control levels of 23 +/- 7% of preocclusion values) and improved recovery at 5 hours postreperfusion (106 +/- 6% vs control levels of 54 +/- 4% of preocclusion values). In animals receiving methylprednisolone immediately prior to reperfusion, there was also similar recovery of segment shortening at 5 hours (97 +/- 3%). In contrast, dogs receiving methylprednisolone 15 minutes after the onset of reperfusion or sodium succinate (5.5 mg/kg, intravenously administered) 90 minutes prior to occlusion demonstrated no improvement in recovery of function. Experiments in dogs not subjected to coronary occlusion documented that methylprednisolone sodium succinate lacked inotropic and vasodilator properties. The results suggest that methylprednisolone administered prior to or during coronary artery occlusion but not after reperfusion enhances the functional recovery of hypokinetic, postischemic, reperfused myocardium. These effects are unrelated to any direct hemodynamic action of steroids or to the sodium succinate salt.

Eleventh Gaddum memorial lecture. Lipocortin and the mechanism of action of the glucocorticoids

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Receptor-mediated effects of glucocorticoids on inflammation: enhancement of the inflammatory response with a glucocorticoid antagonist

Glucocorticoids suppress the inflammatory response by altering leukocyte traffic and function, cytokine secretion and action, and phospholipid metabolism. We employed the glucocorticoid receptor antagonist RU 486, to examine whether glucocorticoids suppress the inflammatory response through a receptor-mediated mechanism and whether basal glucocorticoid secretion exerts antiinflammatory effects in the resting (non-stress) state. To test these hypotheses we evaluated the effects of increasing doses of dexamethasone, RU 486, or dexamethasone plus RU 486 on the exudate volume and concentrations of leukocytes, prostaglandin E2, (PGE2) and leukotriene B4 (LTB4) in intact rats that received subcutaneous carrageenin. Exudate volume, leukocyte concentration and LTB4 and PGE2 levels were all suppressed by dexamethasone in a dose-dependent fashion (P less than 0.005). RU 486 was able to antagonize fully the suppressive effects of dexamethasone on the inflammatory response (P less than 0.001) and to cause increases of exudate volume and leukocyte, PGE2 and LTB4 concentrations when given alone (P less than 0.05). These increases ranged between 30 and 100% above the basal inflammatory response. We conclude that glucocorticoids most likely suppress the inflammatory response by a glucocorticoid receptor-mediated mechanism and under basal conditions exert tonic antiinflammatory effects.

Decreased gastro-intestinal responses to salbutamol and serotonin in streptozotocin-induced diabetes: improving effect of insulin in vivo and in vitro

1. Decreased gastro-intestinal responses to salbutamol (sal) and serotonin (5-HT) in experimental diabetes have been postulated. The present study was designed to investigate whether in vivo and in vitro insulin treatments improve the decreased gastro-intestinal responses. 2. In vivo insulin treatment (166.7 micrograms/kg/day i.p.) for 6 weeks is able to improve both decreased gastro-intestinal beta-adrenergic and serotonergic responses. 3. Insulin incubation in bathing medium for 4-5 hr enhances the decreased gastro-intestinal responses to sal, but not to 5-HT. 4. The above results strongly suggest that the improving effect of insulin on the gastro-intestinal beta-adrenergic responses is direct in nature. In contrast, the improving effect on insulin on the serotonergic responses occurs via an indirect mechanism.

Suppression of yeast ingestion by dexamethasone in macrophage cultures: evidence for a steroid-induced phagocytosis inhibitory protein

The mechanism by which glucocorticoid steroids suppress yeast phagocytosis in cultures of resident and thioglycollate-elicited murine peritoneal macrophages was examined. Time course and dose-response studies demonstrated that the phagocytic capacity of resident macrophages was suppressed by dexamethasone to the same extent in both newly established cultures and cultures that were incubated for several days. In contrast, relative to newly established cultures of elicited cells that were treated with the drug, elicited macrophages that were incubated for at least 1 day prior to exposure to dexamethasone, exhibited enhanced sensitivity to the action of the steroid. Steroid-induced phagocytic inhibitory responses were blocked by the metabolic inhibitors cycloheximide and actinomycin D. The suppression of phagocytosis by dexamethasone was mediated by a factor, present in the cellular homogenates of steroid-treated macrophages, that was partially purified by Sephadex G-25 chromatography. Since the phagocytic inhibitory activity in these homogenates was destroyed following exposure to heat and trypsin, the factor has been named phagocytosis inhibitory protein (PIP). The antiphagocytic activity of PIP was neutralized by treatment with RM23, a monoclonal antibody directed against lipocortin. The results support the hypothesis that the suppression of yeast ingestion is mediated by the action of PIP, which is induced in dexamethasone-treated macrophage cultures. Moreover, PIP appears to belong to the lipocortin family of phospholipase inhibitory proteins.

Binding of dexamethasone and its effect on histamine release from rat mast cells

Purified rat peritoneal mast cells were incubated for 20 h with or without dexamethasone (4 x 10(-6) M) and then passively sensitized with serum from Trichinella spiralis-infected rats. The release of histamine using various secretagogues (concanavalin A, crude antigen of T. spiralis and polymyxin B) was determined. Dexamethasone treatment markedly inhibited IgE-dependent release of histamine (from 33.9 +/- 5.0% to 12.4 +/- 5.1% and from 39.8 +/- 7.9% to 14.2 +/- 6.5% of total cellular histamine content, respectively) whereas histamine release stimulated by the nonimmunological stimulus, polymyxin B was unaffected by this steroid. This suggests that the effects of dexamethasone cannot be exclusively explained by inhibition of phospholipases. Specific binding of 3H-dexamethasone to purified mast cells displayed sigmoidal dependence on concentration which may be the result of either negative cooperativity or the presence of a different class of binding sites. Two saturation plateaux at 20-30 x 10(-9) M and 70-90 x 10(-9) M were observed. The equilibrium dissociation constant for the higher affinity binding sites was Kd1 = 1.9 x 10(-8) M and represented 25,290 sites/cell, whereas the apparent Kd2 for lower affinity sites amounted to 5.5 x 10(-8) M and represented about 120,000 sites/cell.

Plasma phospholipid essential fatty acids and prostaglandins in alcoholic, habitually violent, and impulsive offenders

Plasma phospholipid essential fatty acids and some of their main metabolites, prostaglandins, were measured among habitually violent and impulsive male offenders, who all had alcohol abuse problems, and nonviolent control persons. Linoleic acid (18:2n-6), the precursor of the n-6 fatty acids, was below normal in intermittent explosive disorder, but the dihomogammalinolenic acid (DGLA) (20:3n-6) and some subsequent n-6 acids were at the same time elevated among all offenders. Also, a monounsaturate, oleic acid (18:1n-9) was elevated. The high DGLA correlated with low cholesterol level in intermittent explosive disorder. The arachidonic acid metabolites PGE2 and TxB2 were elevated in violent antisocial personality. The PGE1/DGLA ratio was low in intermittent explosive disorder. The number of registered violent crimes and violent suicidal attempts correlated with high phospholipid DGLA values. The possibility that the high phospholipid DGLA is connected with low free DGLA pool, and therefore low PGE1 formation, among these offenders is discussed.

Glucocorticoids and head injury. A possible participation of lipocortin (lipomodulin) in actions of the steroid hormones

The actions of glucocorticoids require the synthesis of new proteins in many, if not all, cases. One such protein that mimics the actions of glucocorticoids has been isolated and characterized as lipocortin. This protein can mimic the anti-inflammatory activity of glucocorticoids by inhibiting phospholipase A2. The effect of glucocorticoids on various stages of brain and spinal cord injury may be partly, although not totally, explained by the activity of lipocortin.

Hydrocortisone inhibits antigen-induced rise in intracellular free calcium concentration and abolishes leukotriene C4 production in leukemic basophils

Antigenic stimulation of rat basophilic leukemia cells (RBL-3H3) elevates intracellular free Ca2+ concentration ([Ca2+]i) and induces production of leukotriene C4 (LTC4). This model was used to examine the role of Ca2+ in LTC4 formation, and inhibition by hydrocortisone (HC). HC, at a physiological concentration (2 x 10(-7) M), selectively prevented the stimulatory effect of the antigen on LTC4 production whereas the response to calcium ionophore (A23187) remained unimpaired. The inhibition by HC was time-dependent: half maximal response was reached at 2 hour and maximal response at 3 hours. Addition of arachidonic acid (3 micrograms/ml) did not overcome the inhibitory action of HC. An elevated [Ca2+]i is known to be essential for the activation of both 5-lipoxygenase and phospholipase A2. The stimulatory effect of the antigen on LTC4 production was abolished when the cells were incubated in Ca2+-deficient medium. Likewise, calcium ionophore stimulation shows dependence on extracellular Ca2+. Half maximal stimulation by the antigen and calcium ionophore was observed at external Ca2+ concentration of 150 microM and 40 microM respectively. Treatment with HC largely prevented the antigen-induced rise in [Ca2+]i, measured by Quin 2. In addition, HC reduced by 70% the accumulation of 45Ca2+ induced by the antigen. Collectively, these results demonstrate for the first time that HC reduces antigen-induced elevation of [Ca2+]i, and this may be associated with the inhibitory action of HC on LTC4 formation. This property could be partly responsible for the antiallergic and antiinflammatory activities of HC.

Regulation of prostaglandin formation by glucocorticoids and their second messenger, lipocortins

Glucocorticoids induce the synthesis of a family of phospholipase inhibitory proteins, lipocortins. This family of lipocortins includes inhibitory proteins on phospholipase A2, phospholipase C and phosphatidylinositol phospholipase C. Hence, glucocorticoids reduce the formation of prostaglandins and leukotrienes by inhibiting cellular phospholipases, enzymes that degrade membrane phospholipids to release arachidonic acid, a precursor. The induction by glucocorticoids requires 1 h for the synthesis of mRNA and 5 h for the synthesis of proteins in various tissues and cells. However, glucocorticoids often exert their suppressive effects before the induction of lipocortins. This is now attributed to the nonenzymic formation of the adducts between glucocorticoids and lipocortins. These adducts are easily inserted into the membranes and more resistant to digestion of proteases, thus being more biologically potent with respect to suppression of the release of arachidonic acid, a precursor of prostaglandins and leukotrienes.

Effects of dexamethasone on prostacyclin biosynthesis in rabbit mesothelial cells

We investigated whether glucocorticoids reduce the formation of arachidonic acid metabolites in a non myeloid cell type, the mesothelial cell, which is functionally and embryologically related to the vascular endothelial cell and which forms almost exclusively prostacyclin from arachidonic acid. Preincubation of rabbit mesothelial cells with 2.5 microM dexamethasone suppressed basal as well as bradykinin- or thrombin-stimulated prostacyclin biosynthesis. In further experiments bradykinin was selected as stimulus. The inhibition by dexamethasone was dose-dependent between 0.025 and 2.5 microM. The minimum contact period required for expression of this effect was 30 min and after a contact period of 60 to 120 min the inhibition reached a maximum, but was never complete. After 240 min, sufficient activity was secreted in the extracellular medium for inhibition of the prostacyclin formation in untreated cells. Experiments with cycloheximide were somewhat confused by its direct effects on prostacyclin biosynthesis, but still suggested that the anti-prostacyclin effect of dexamethasone required de novo protein biosynthesis. Our experiments indicate that glucocorticoids induce the formation of lipocortin-like factor(s) in non-phagocytic mesothelial cells, thereby suppressing the formation of prostacyclin, their main arachidonic metabolite.

Dexamethasone-induced stimulation of arachidonic acid release by U937 cells grown in defined medium

Since the presence of serum in culture media has been shown to alter prostaglandin production, as well as to interfere with the action of anti-inflammatory drugs, we have studied the effect of dexamethasone, a potent steroidal anti-inflammatory drug, on the metabolism of arachidonic acid by human monocyte-like cells (U937) grown in a fully defined medium. Under these culture conditions, dexamethasone (10(-6) M, 24 h) induced a marked stimulation of the release of unmetabolized arachidonic acid into the culture medium. The steroid also induced an inhibition of cell proliferation which became significant only after 48 h of treatment. The accumulation of arachidonic acid in the medium after steroid treatment was associated with a significant inhibition of cell acyltransferase activity, suggesting that steroids may also act upon arachidonic acid metabolism at sites other than those of phospholipase activity.

Dexamethasone inhibits prostaglandin release from rabbit coronary microvessel endothelium

The effects of dexamethasone on prostaglandin secretion by cultivated rabbit coronary microvascular endothelial (RCME) cells were investigated. Incubation of RCME cells with dexamethasone resulted in a time- and concentration-dependent decrease in prostaglandin accumulation in the culture media and reduced basal and A23187-stimulated prostaglandin (PG) E2 and 6-keto-PGF1 alpha release. The maximal effects of dexamethasone (50-80% inhibition) were achieved after 16-18 h of incubation with the steroid at a final concentration of 10(-7) M. The effects of dexamethasone treatment were partially reversed 24 h after removal of the steroid from the culture media. Dexamethasone treatment did not reduce arachidonic acid-stimulated prostaglandin synthesis, indicating that the level of inhibition was proximal to that of cyclooxygenase. The inhibitory effects of dexamethasone could be prevented by pretreatment of the RCME cells with actinomycin D or cycloheximide, suggesting a requirement for protein synthesis in the inhibitory action of dexamethasone. Conditioned media from dexamethasone-treated cells contained a factor that inhibited porcine pancreatic phospholipase A2 (PLA2) in vitro. Transfer of conditioned media from dexamethasone-treated cells to untreated cells did not reduce basal or stimulated prostaglandin release; in contrast, a stimulatory action was consistently observed. Adherence of rabbit peripheral polymorphonuclear leukocytes (PMN) to RCME cells was reduced when the leukocytes were pretreated with 10(-7) M dexamethasone (4 h). However, dexamethasone pretreatment of the RCME cells did not significantly effect granulocyte adhesion. Thus coronary microvascular endothelial cell prostaglandin production is regulated by glucocorticoids, and glucocorticoid-pretreated microvascular endothelial cell release an inhibitor of PLA2 activity into the culture media.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of action of glucocorticosteroids. Inhibition of T cell proliferation and interleukin 2 production by hydrocortisone is reversed by leukotriene B4

The mechanism whereby glucocorticosteroids are immunosuppressive is unknown. One potential mechanism of action of these compounds is inhibition of arachidonic acid metabolism. We found that the inhibition of lymphocyte proliferation by hydrocortisone or dexamethasone was mimicked by nonspecific lipoxygenase inhibitors and also by a specific 5-lipoxygenase inhibitor, but not by a specific cyclooxygenase inhibitor. Mitogen-stimulated cultures of T cells produce approximately 5 X 10(-9) M leukotriene B4 (LTB4) in 24 h. This production of LTB4 is completely inhibited by concentrations of hydrocortisone or lipoxygenase inhibitors that inhibit mitogen-induced [3H]thymidine incorporation. The inhibition of lymphocyte proliferation by either hydrocortisone or by the 5-lipoxygenase inhibitor was totally reversed by LTB4 but not by leukotriene C4 or leukotriene D4. LTB4 had no effect on the inhibition of lymphocyte proliferation by noncorticosteroids such as prostaglandin E2, histamine, or gamma-interferon. The inhibition of interleukin 2 (IL-2) production by hydrocortisone or dexamethasone was also completely reversed by exogenous LTB4. LTB4 alone did not cause IL-2 production or cell proliferation when added to resting lymphocytes. Thus, endogenous LTB4 production appears to be necessary but not sufficient for phytohemagglutinin-induced IL-2 production and lymphocyte proliferation. Glucocorticosteroids inhibit IL-2 production and lymphocyte proliferation by inhibiting endogenous LTB4 production.