Interference of corticosteroids with prostaglandin E2 synthesis at the level of cyclooxygenase-2 mRNA expression in kidney cells

Synergistic induction of osteopontin by aldosterone and inflammatory cytokines in mesangial cells

Hypertensive nephrosclerosis is characterized by activation of the renin-angiotensin-aldosterone system in combination with an inflammatory response characterized by an infiltration of T-cells and mononuclear cells, which release proinflammatory cytokines like IL-1beta/TNFalpha. In various models of experimental hypertensive disease the chemokine osteopontin (OPN) enhances further leukocyte infiltration. Therefore, we investigated the induction of OPN expression in renal mesangial cells (MCs) by aldosterone and the inflammatory cytokines IL-1beta/TNFalpha. Incubation with aldosterone resulted in a time- and concentration-dependent increase in OPN mRNA and protein. OPN mRNA expression followed a biphasic time course with an early increase between 4 and 8 h and the second phase starting at 14 h. The early phase was independent of protein synthesis, indicating a direct effect of aldosterone. Aldosterone-mediated induction of OPN was prevented by spironolactone, indicative of a receptor-mediated aldosterone effect. The mineralocorticoid receptor (MR) was identified in MCs by RT-PCR and immunoprecipitation, and shown to interact with a putative aldosterone-response element of the OPN promoter. The proinflammatory cytokines IL-1beta and TNFalpha only marginally affected OPN expression in MCs. However, coincubation of aldosterone and the cytokines synergistically increased OPN mRNA and protein levels. Since the synergistic effect on OPN mRNA was inhibited by diphenyleneiodonium, we assume an involvement of reactive oxygen species (ROS). We conclude that the chemokine OPN is a target gene of aldosterone in renal MCs, which is activated via the MR, and that proinflammatory cytokines enhance aldosterone-dependent OPN expression. In vivo, this may result in further leukocyte infiltration aggravating hypertensive nephrosclerosis.

The role of female gonadal hormones in behavioral sex differences in persistent and chronic pain: Clinical versus preclinical studies

Clinical and preclinical studies have found sex-specific differences in the discrimination and perception of nociceptive stimuli. This article reviews the current literature concerning the biological basis of sex differences in the behavioral response to persistent inflammatory and chronic pain stimuli. The emerging picture from both clinical and preclinical studies suggests that the basis of these differences in nociceptive responses to such stimuli resides in the regulatory activity of gonadal hormones in the central nervous system. Published reports suggest that pain management targeted at female patients should consider hormonal factors during the female reproductive cycle.

Corticosteroids in sepsis: from bench to bedside?

The use of corticosteroids in patients with septic shock has been recently revisited and the use of low dose corticosteroids led to very promising results, particularly in patients with corticosteroid insufficiency. We review the different mechanisms that can account for their beneficial effects in patients. Glucocorticoids display a wide spectrum of anti-inflammatory properties that have been identified in in vitro and in vivo experimental models (e.g., inhibition of production of pro-inflammatory cytokines, free radicals, prostaglandins and inhibition of chemotaxis, and adhesion molecule expressions.) In addition, glucocorticoids have profound effects on the cardiovascular system (e.g., increasing mean blood pressure, increasing pressor sensitivity, and therefore decreasing the duration of use of catecholamines during septic shock.) Through these anti-inflammatory and cardiovascular effects, low doses of glucorticoids may improve septic shock survival.

Mineralocorticoid regulation of cyclooxygenase-2 expression in rat renal medulla

The renal inner medulla and its distal one-third, the papilla, are major sites of prostanoid synthesis involved in water and electrolyte homeostasis. These sites contain variable levels of cyclooxygenase (COX)-2, a key prostaglandin synthase enzyme that is sensitive to adrenal steroids. Immunoreactive renal medullary COX-2, restricted to interstitial cells in control adult rats, shows a gradient of intense staining at the tip of the papilla that gradually diminishes to undetectable levels in the proximal inner medulla. We used adrenalectomy (ADX) and steroid replacement to investigate the effects of steroids on papillary COX-2. Immunoblots demonstrate that papillary COX-2 was reduced by one-half after 2 wk ADX; glucocorticoid replacement ameliorated the decline but not to control levels. Mineralocorticoid (deoxycorticosterone acetate; DOCA) replacement stimulated papillary COX-2 more than fivefold over control; both the intensity of immunostaining and the numbers of COX-2-positive cells in the inner medulla increased. Similar stimulation of papillary COX-2 resulted from DOCA treatment of normal control rats, but the response was blunted in rats fed a low-salt diet and absent in Brattleboro rats. DOCA treatment of mouse renal medullary interstitial cells in culture had no effect, but increased tonicity of the culture medium with NaCl caused strong upregulation of COX-2. Urea, a permeant molecule, had no effect. Together, these results suggest that mineralocorticoids lead to upregulation of COX-2 in rat renal medulla by indirect pathways, probably involving induced electrolyte hypertonicity in the interstitial fluid.

Cyclo-oxygenase-2 inhibitors and the kidney: a case for caution

Cyclo-oxygenase (COX) is one of the key enzymes in the biosynthesis of prostaglandins. Two isoforms of this enzyme COX-1 and COX-2 are known to exist. Among other functions, prostaglandins play an important role in the protection of the gastric mucosa and maintenance of renal function in pathophysiological conditions which would otherwise threaten it. Conventional nonsteroidal anti-inflammatory drugs (NSAIDs) block prostaglandin synthesis, resulting in gastric mucosal injury and renal dysfunction in susceptible individuals. The recent introduction of selective COX-2 inhibitors, celecoxib and rofecoxib, appear to induce less gastrointestinal morbidity. Although conclusive data are still lacking, there is evidence to suggest that COX-2 antagonists may be capable of causing some of the same renal syndromes seen in association with the older, less selective NSAIDs.

Effect of angiotensin II on rat renal cortical 11beta-hydroxysteroid dehydrogenase

Renal 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) are subject to modulation by various endogenous factors. 11beta-HSDs convert glucocorticoids into inactive 11-ketones and thereby determine tissue levels of active glucocorticoids and thus the extent of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation. As such, modulation of the activity of renal 11beta-HSDs may contribute to the cascade of regulatory events involved in renal electrolyte water handling. We investigated whether renal 11beta-HSDs are modulated by elevated circulating angiotensin II. In rats infused for 2 wk with angiotensin II (250 ng/[kg x min] subcutaneously), plasma angiotensin II, aldosterone, and corticosterone were raised 5.1-, 10.7-, and 2.3-fold, respectively, compared with control rats. Angiotensin II infusion raised corticosterone 11beta-oxidation 1.46- and 1.35-fold in renal cortical proximal and distal tubules (enriched by Percoll centrifugation), respectively, but had no effect on 11beta-HSD1 and 11beta-HSD2 mRNA levels (semiquantitative reverse transcriptase polymerase chain reaction), except for distal tubular 11beta-HSD1 mRNA, which was decreased to 50%. In vitro treatment of freshly isolated tubules with angiotensin II for 45 min prior to assessment of 11beta-HSD activity showed no direct acute effects of angiotensin II on tubular corticosterone 11beta-oxidation. The enhanced renal tubular corticosterone 11beta-oxidation in vivo may partly protect renal GR and MR from elevated plasma corticosterone on angiotensin II infusion.

Endocrine and paracrine regulation of birth at term and preterm

We have examined factors concerned with the maintenance of uterine quiescence during pregnancy and the onset of uterine activity at term in an animal model, the sheep, and in primate species. We suggest that in both species the fetus exerts a critical role in the processes leading to birth, and that activation of the fetal hypothalamic-pituitary-adrenal axis is a central mechanism by which the fetal influence on gestation length is exerted. Increased cortisol output from the fetal adrenal gland is a common characteristic across animal species. In primates, there is, in addition, increased output of estrogen precursor from the adrenal in late gestation. The end result, however, in primates and in sheep is similar: an increase in estrogen production from the placenta and intrauterine tissues. We have revised the pathway by which endocrine events associated with parturition in the sheep come about and suggest that fetal cortisol directly affects placental PGHS expression. In human pregnancy we suggest that cortisol increases PGHS expression, activity, and PG output in human fetal membranes in a similar manner. Simultaneously, cortisol contributes to decreases in PG metabolism and to a feed-forward loop involving elevation of CRH production from intrauterine tissues. In human pregnancy, there is no systemic withdrawal of progesterone in late gestation. We have argued that high circulating progesterone concentrations are required to effect regionalization of uterine activity, with predominantly relaxation in the lower uterine segment, allowing contractions in the fundal region to precipitate delivery. This new information, arising from basic and clinical studies, should further the development of new methods of diagnosing the patient at risk of preterm labor, and the use of scientifically based strategies specifically for the management of this condition, which will improve the health of the newborn.

Regulation of cyclooxygenase-2 (COX-2) in rat renal cortex by adrenal glucocorticoids and mineralocorticoids

Production of prostaglandins involved in renal salt and water homeostasis is modulated by regulated expression of the inducible form of cyclooxygenase-2 (COX-2) at restricted sites in the rat renal cortex. Because inflammatory COX-2 is suppressed by glucocorticoids, and prostaglandin levels in the kidney are sensitive to steroids, the sensitivity of COX expression to adrenalectomy (ADX) was investigated. By 2 weeks after ADX in mature rats, cortical COX-2 immunoreactivity increased 10-fold in the cortical thick ascending limb and macula densa. The constitutive isoform, COX-1, was unchanged. The magnitude of the changes and specificity of COX-2 immunoreactivity were validated by in situ hybridization histochemistry of COX-2 mRNA and Western blot analysis. Increased COX-2 activity (>5-fold) was documented by using a specific COX-2 inhibitor. The COX-2 up-regulation in ADX rats was reversed by replacement therapy with either corticosterone or deoxycorticosterone acetate. In normal rats, inhibition of glucocorticoid receptors with RU486 or mineralocorticoid receptors with spironolactone caused up-regulation of renal cortical COX-2. These results indicate that COX-2 expression in situ is tonically inhibited by adrenal steroids, and COX-2 is regulated by mineralocorticoids as well as glucocorticoids.

Opiate, cannabinoid, and eicosanoid signaling converges on common intracellular pathways nitric oxide coupling

Scientific fields as they emerge initially appear to be unrelated to other projects even if they are in a similar area of interest. This is especially true in the case of opiate, cannabinoid, and eicosanoid signaling processes. In this limited speculative review, we attempt to examine aspects of their intracellular cascading signaling systems for their commonalities. We find intracellular calcium mobilization, nuclear factor kappa B involvement, adenylate cyclase activity, and, finally, constitutive nitric oxide release to be converging points for these signaling processes, occurring by separate and distinct receptor-mediated effector systems. Phosphokinase C, mitogen activated protein kinase, and cytosolic phospholipase A2 also represent points of common impact. In this regard, aspirin also appears to be involved in an aspect of this signaling convergence. We conclude that many of the physiological observations regarding the actions of these signaling molecules, for example, immunosuppression, neurotransmission, vasodilation, cellular adherence, and cytotoxicity, can now be understood by considering their converging biochemical cascades.

Lipopolysaccharide-induced expression of cyclooxygenase-2 in mouse macrophages is inhibited by chloromethylketones and a direct inhibitor of NF-kappa B translocation

In macrophages, cyclooxygenase-2 (COX-2) is induced by cytokines, mitogens, or endotoxin. The present study investigates whether inhibitors of the nuclear transcription factor NF-kappa B affect lipopolysaccharide (LPS)-mediated expression of COX-2 mRNA, protein, and activity in the macrophage cell line J774.1A. The activation of COX-2 was assessed by measuring the accumulation of prostaglandin (PG) E2 by radioimmunoassay. Expression of COX-2 mRNA and protein was detected by Northern and Western blot analysis, respectively. In the absence of LPS, mouse macrophages did not express COX-2 and generated low amounts of prostaglandin (PG) E2. Treatment of J774.1A with LPS (0.1-30 micrograms/ml) caused expression of COX-2 protein and activity. Induction of COX-2 activity along with the induction of COX-2 mRNA and protein by LPS was attenuated by the serine protease inhibitors N-alpha-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and N-alpha-tosyl-L-lysine chloromethyl ketone (TLCK). A cell permeable peptide and a direct inhibitor of NF-kappa B translocation, SN50, attenuated the accumulation of PGE2 in cell supernatant in a concentration-dependent manner. Our results show that induction of COX-2 by LPS in macrophages involves activation of NF-kappa B and point to a possible therapeutic use of protease inhibitors in inflammatory processes.

Effect of hormonal status on the expression of the cyclooxygenase 1 and 2 genes and prostaglandin synthesis in rat mammary glands

Hormonal effects on mammary carcinogenesis have been linked to prostaglandin (PG) synthesis. The purpose of the present study was to examine the expression of the cyclooxygenase (COX) 1 and 2 genes and levels of PG synthesis in the mammary glands of rats that have different levels of susceptibility to mammary gland carcinogenesis associated with pregnancy, lactation, post-lactation involution, and ovariectomy. The expression of COX-1 mRNA, measured by Northern blot analysis, was similar in virgin, lactating, pregnant, and post-lactational animals of the same age. Ovariectomized animals exhibited significantly lower levels of COX-1 mRNA (approximately 40%) compared to the sham-operated controls or the ovariectomized animals treated with estradiol and progesterone. COX-2 mRNA, measured by RT-PCR, was detectable only in the mammary glands of lactating animals and ovariectomized animals administered estradiol and progesterone. Induction on COX-2 expression occurred in both stromal and epithelial cells in lactating rat mammary glands. COX enzymatic activities, determined by measuring the conversion rate of [1-14 C]-arachadonic acid to prostanoids, showed that lactating animals had a significantly higher activity compared to virgin (approximately 40%), pregnant (approximately 30%), or postlactational animals (approximately 40%). Ovariectomized animals had significantly lower COX enzymatic activity compared to the sham operated animals. Significant induction of COX activity, however, was observed in ovariectomized animals administered estradiol and progesterone. These changes in COX enzymatic activity were paralleled by similar changes in the mammary gland PGE2 content, measured by enzyme immunoassay. Our results suggest that the effect of hormones on the genesis of mammary cancer in the rat may be mediated, at least in part, by their effects on COX-2 expression and PG synthesis.

Effects of Tripterygium wilfordii hook F extracts on induction of cyclooxygenase 2 activity and prostaglandin E2 production

OBJECTIVE

Extracts of the Chinese herbal remedy Tripterygium wilfordii Hook F (TWHF) have been reported to be effective in the treatment of patients with a variety of inflammatory and autoimmune diseases, but the mechanism of this therapeutic effect has not been completely delineated. The present study was designed to assess the effects of TWHF on the in vitro synthesis of prostaglandin E2 (PGE2) and on the expression of the cyclooxygenase isoforms, COX-1 and COX-2, in various human cell types.

METHODS

Monocytes from human peripheral blood (HM), fibroblasts from rheumatoid arthritis synovial tissue (RASF), human neonatal foreskin fibroblasts (HFF), and the histiocytic cell line U937 were cultured for designated time periods with or without lipopolysaccharide (LPS), and in the presence or absence of varying concentrations of the following inhibitors: the methanol/chloroform (T2) extract of TWHF, the ethyl acetate (EA) extract of TWHF, a purified diterpenoid component of TWHF (triptolide), dexamethasone, and indomethacin. Culture supernatants were harvested for PGE2 content assays. Total RNA was extracted from the cells and analyzed for COX-1 and COX-2 messenger RNA (mRNA) expression using reverse transcriptase-polymerase chain reaction or Northern blotting.

RESULTS

Both the T2 and EA extracts inhibited PGE2 synthesis in the LPS-stimulated HM, RASF, and HFF cells, which was reflected by a marked suppression in the levels of mRNA for COX-2. In contrast, neither extract inhibited PGE2 production in U937 cells that did not express COX-2. Triptolide also inhibited LPS-stimulated induction of COX-2 mRNA and synthesis of PGE2, at the same inhibitory concentration as seen with the EA extract. The effects of T2, EA, and triptolide paralleled the inhibitory action of dexamethasone.

CONCLUSION

The data indicate that both the T2 and EA extracts of TWHF, as well as the triptolide component, inhibit PGE2 production in a variety of human cells by blocking the up-regulation of COX-2.