Human dental pulp cells exhibit bone cell-like responsiveness to fluid shear stress

Background aimsFor engineering bone tissue to restore, for example, maxillofacial defects, mechanosensitive cells are needed that are able to conduct bone cell-specific functions, such as bone remodelling. Mechanical loading affects local bone mass and architecture in vivo by initiating a cellular response via loading-induced flow of interstitial fluid. After surgical removal of ectopically impacted third molars, human dental pulp tissue is an easily accessible and interesting source of cells for mineralized tissue engineering. The aim of this study was to determine whether human dental pulp-derived cells (DPC) are responsive to mechanical loading by pulsating fluid flow (PFF) upon stimulation of mineralization in vitro.MethodsHuman DPC were incubated with or without mineralization medium containing differentiation factors for 3 weeks. Cells were subjected to 1-h PFF (0.7 ± 0.3Pa, 5Hz) and the response was quantified by measuring nitric oxide (NO) and prostaglandin E₂ (PGE₂) production, and gene expression of cyclooxygenase (COX)-1 and COX-2.ResultsWe found that DPC are intrinsically mechanosensitive and, like osteogenic cells, respond to PFF-induced fluid shear stress. PFF stimulated NO and PGE₂ production, and up-regulated COX-2 but not COX-1 gene expression. In DPC cultured under mineralizing conditions, the PFF-induced NO, but not PGE₂, production was significantly enhanced.ConclusionsThese data suggest that human DPC, like osteogenic cells, acquire responsiveness to pulsating fluid shear stress in mineralizing conditions. Thus DPC might be able to perform bone-like functions during mineralized tissue remodeling in vivo, and therefore provide a promising new tool for mineralized tissue engineering to restore, for example, maxillofacial defects.     

T cell recruitment from the thymus to the spleen in tumor-bearing mice

Summary After inoculation of tumor cells (methylcholanthrene-induced sarcoma), the number of Thy 1⁺ cells and PNA (peanut agglutinin) binding cells, which were shown to be different subpopulations were increased in the spleen of thymus-intact mice, in contrast this increase was not observed in adult thymectomized mice. In experiments performed concurrently with splenic cell analysis, we found that the plasma PGE₂ levels declined in parallel with the tumor growth. Prevention of such a decline of plasma PGE₂ level by replenishment with exogenous PGE₂ inhibited the splenic cell increase in tumor bearers. In the tumorbearing mice, cell traffic systems from the thymus to the periphery was ascertained by injecting fluorescein diacetate (FDA) into the thymus and observing fluorescein positive cells in the periphery. We suggest that increased recruitment of thymic cells to the periphery may be mediated by PGE₂ in the presence of a tumor.Abbreviations PNA⁺ cells, peanut agglutinin binding cells - Ig⁺ cells, surface IgM positive cells - Thy 1⁺ Thy 1.2 antigen positive cells - PGE₂ prostaglandin E₂     

PGE2 involvement in experimental infection with Trypanosoma cruzi subpopulations

PGE₂ involvement in experimental Trypanosoma cruzi infection depends on the lethal capacity of the parasite subpopulation used. Mice acutely infected with non-lethal K98 displayed an enhancement in PGE₂ serum levels during the acute period, while those infected with lethal T. cruzi subpopulations (RA or K98-2) showed levels not different from normal mice. The enhancement detected in K98 group could be related both to an increased number of CD8+ T cell number and to enhanced PGE₂ release per cell by CD8+; values of PGE₂ release by adherent cells were not altered in this group. Treatment with cyclooxygenase inhibitors enhanced mortality rates of mice infected with K98, and administration of 16,16-dimethyl PGE₂ (dPGE) reversed this effect. However, mice infected with RA did not reduce their mortality rates by administration of diverse doses of dPGE. These findings suggest that PGE₂ could play a role in resistance in mice infected with K98.     

Heterogeneity of murine adherent interleukin-2-activated killer cells differential effect of prostaglandin E2 and forskolin

We have studied the relationship between cytotoxic activity, size and granularity of murine interleukin-2-activated adherent killer cells issued from spleen cells cultured with high levels of IL-2. The effects of prostaglandin E₂ (PGE₂) and forskolin upon these cells were assessed. All adherent spleen cells obtained after 5 days of culture were large granular lymphocytes but presented a heterogeneity in size and granularity. After fractionation on a discontinuous-density Percoll gradient, four cellular subpopulations were isolated. Fluorescence-activated cell sorting analysis showed that cells of the lightest fraction (F1) were the largest, while the cells found in the heaviest fraction (F4) were much more granular than the cells collected in the two intermediate fractions (F2 and F3). The serine esterases level was higher in F4 than in unfractionated cells and diminished to about 40% in cells of fractions F2 and F3, which expressed a cytotoxic activity against YAC-1 cells higher than that in unfractionated cells or in F1 or F4, which presented the lowest cytotoxic activity. When AK cells were cultured for 48 h in the presence of either PGE₂ or forskolin, which induce an intracellular increase of cAMP, we observed that PGE₂ (1M) inhibited the cytotoxic activity, but surprisingly forskolin (2M) exerted a stimulating effect on the induction of cytotoxic activity. After fractionation on a discontinuous Percoll gradient we observed the same cellular distribution among PGE₂ or forskolin-treated or-untreated cells, but PGE₂ induced an increase of size and granularity. This effect of PGE₂ was more potent on the cells collected in F4. However this variation of granularity was not associated with any variation in the serine esterase level. The cytotoxic activity of PGE₂- or forskolin-treated cells did not present any significant variation relative to the control for cells collected in F2 and F3: on the other hand, forskolin-treated cells collected in F4 showed a significantly higher cytotoxicity than did the corresponding untreated or PGE₂-treated cells.     

Phorbol esters inhibit chondrogenesis in limb mesenchyme by mechanisms independent of PGE2 or cyclic AMP

Effects of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on chondrogenesis and concentrations of prostaglandin E₂ (PGE₂) and cyclic AMP (cAMP) were investigated in micromass cultures of chick limb mesenchyme derived from the distal tip of stage 25 limb buds. TPA completely inhibited Chondrogenesis during the first 4 days of culture; however, a few small cartilage nodules formed by day 6. Relative to control cultures, both PGE₂ and cAMP concentrations were altered by TPA treatment during the 6-day period of cell culture. Concentrations of both compounds increased in control cells during the first 24 h of culture and then declined during the remaining 5 days. In TPA-treated cells both PGE₂ and cAMP levels increased progressively during the 6 days of cell culture, each being elevated at day 6 by twofold over control cells. The results suggest the presence of regulatory pathways important in Chondrogenesis which occur independent of those initiated by PGE₂ and the cAMP system.     

Regulation of prostaglandin production by osteoblast-rich calvarial cells

The effect of various factors upon prostaglandin (PG) production by the osteoblast was examined using osteoblast-rich populations of cells prepared from newborn rat calvaria. Bradykinin and serum, and to a lesser extent, thrombin, were also shown to stimulate PGE₂ and 6-keto-PGF_1α (the hydration product of PGI₂) secretion by the osteoblastic cells. Several inhibitors of prostanoid synthesis, dexamethasone, indomethacin, dazoxiben and nafazatrom, were tested for their effects on the calvarial cells. All inhibited PGE₂ and PGI₂ (the major arachidonic acid metabolites of these cells) production with half-maximal inhibition by all four substances occuring at approximately 10⁻⁷ M. For dazoxiben and nafazatrom, this was in contrast to published results from experiments which have indicated that the compounds stimulated PGI₂ production. Finally, since the osteoblasts is responsive to bone-resorbing hormones, these were tested. Only epidermal growth factor (EGF) was shown to modify PG production. At early time EGF stimulated PGE₂ release, however, the predominant effect of the growth factor was an inhibition of both PGE₂ and PGI₂ production by the osteoblastic cells. The present results suggest that the bone-resorbing hormones do not act to cause an increase in PG by the esteoblast and that any increase in PG production by these cells may be in response to vascular agents     

Role of the blood–cerebrospinal fluid barrier transporter as a cerebral clearance system for prostaglandin E2 produced in the brain

An increasing level of prostaglandin (PG) E₂ is involved in the progression of neuroinflammation induced by ischemia and bacterial infection. Although an imbalance in the rates of production and clearance of PGE₂ under these pathological conditions appears to affect the concentration of PGE₂ in the cerebrospinal fluid (CSF), the regulatory system remains incompletely understood. The purpose of this study was to investigate the cellular system of PGE₂ production via microsomal PGE synthetase‐1 (mPGES‐1), the inducible PGE₂‐generating enzyme, and PGE₂ elimination from the CSF via the blood–CSF barrier (BCSFB). Immunohistochemical analysis revealed that mPGES‐1 was expressed in the soma and perivascular sheets of astrocytes, pia mater, and brain blood vessel endothelial cells, suggesting that these cells are local production sites of PGE₂ in the CSF. The in vivo PGE₂ elimination clearance from the CSF was eightfold greater than that of d ‐mannitol, which is considered to reflect CSF bulk flow. This process was inhibited by the simultaneous injection of unlabeled PGE₂ and β‐lactam antibiotics, such as benzylpenicillin, cefazolin, and ceftriaxone, which are substrates and/or inhibitors of organic anion transporter 3 (OAT3). The characteristics of PGE₂ uptake by the isolated choroid plexus were at least partially consistent with those of OAT3. OAT3 was able to mediate PGE₂ transport with a Michaelis–Menten constant of 4.24 μM. These findings indicate that a system regulating the PGE₂ level in the CSF involves OAT3‐mediated PGE₂ uptake by choroid plexus epithelial cells, acting as a cerebral clearance pathway via the BCSFB of locally produced PGE₂.     

The prostaglandin EP4 receptor is a master regulator of the expression of PGE2 receptors following inflammatory activation in human monocytic cells

Prostaglandin E₂ (PGE₂) is responsible for inflammatory symptoms. However, PGE₂ also suppresses pro-inflammatory cytokine production. There are at least 4 subtypes of PGE₂ receptors, EP1–EP4, but it is unclear which of these specifically control cytokine production. The aim of this study was to determine which of the different receptors, EP1R–EP4R modulate production of tumor necrosis factor-α (TNF-α) in human monocytic cells.Human blood, or the human monocytic cell line THP-1 were stimulated with LPS. The actions of PGE₂, alongside selective agonists of EP1–EP4 receptors, were assessed on LPS-induced TNF-α, IL-1β and IL-10 release. The expression profiles of EP2R and EP4R in monocytes and THP-1 cells were characterised by RT-qPCR. In addition, the production of cytokines was evaluated following knockdown of the receptors using siRNA and over-expression of the receptors by transfection with constructs.PGE₂ and also EP2 and EP4 agonists (but not EP1 or EP3 agonists) suppressed TNF-α production in blood and THP-1 cells. LPS also up regulated expression of EP2R and EP4R but not EP1 or EP3. siRNA for either EP2R or EP4R reversed the suppressive actions of PGE₂ on cytokine production and overexpression of EP2R and EP4R enhanced the suppressive actions of PGE₂.This indicates that PGE₂ suppression of TNF-α by human monocytic cells occurs via EP2R and EP4R expression. However EP4Rs also control their own expression and that of EP2 whereas the EP2R does not affect EP4R expression. This implies that EP4 receptors have an important master role in controlling inflammatory responses.     

Apoptosis-modulating effect of prostaglandin E<Subscript>2</Subscript> in coelomocytes of holothurian <Emphasis Type="Italic">Eupentacta fraudatrix</Emphasis> depends on the cell antioxidant enzyme status

The effects of prostaglandin PGE₂ on apoptosis and antioxidant enzyme activities were studied in two coelomocyte fractions of holothurian Eupentacta fraudatrix in vitro and in vivo. PGE₂ (10^?8–10^?6M) modulated apoptosis in a time-and concentration-dependent manner in both fractions studied in vitro. In vivo, PGE₂ induced apoptosis at concentrations of 0.1–1 μg/g in the fraction enriched with morula-like cells. Phagocytes were more sensitive to the regulating effect of PGE₂. In this fraction, PGE₂ induced apoptosis at concentrations from 0.01 to 1 μg/g, while PGE₂ at 10 μg/g demonstrated an antiapoptotic effect. In all experiments, apoptosis development was accompanied by a disbalance of the antioxidant enzyme system, primarily, decreased catalase activity.     

Limitation of macrophage production in long-term marrow cultures containing prostaglandin E

Addition of prostaglandin E₂ (PGE₂) significantly altered the cellular composition of murine long-term bone marrow cultures. After 4–5 weeks of culture, increased cellularity in the suspension phase was observed in all cultures containing prostaglandin. These suspension cells contained markedly higher proportions of differentiated neutrophils than did cells cultured in the absence of PGE₂. Granulocyte-macrophage progenitor cell levels in the suspension layer were increased 3–20 fold after five weeks in prostaglandin-containing cultures compared with control cultures. Fewer cells comprised the adherent layer in cultures containing prostaglandin. The number of macrophages in this layer was reduced 3–8 fold in these cultures compared with control cultures, while the number of granulocytes was increased 2–3 fold. The progenitor cells biased toward macrophage development were selectively inhibited in the cultures with PGE₂. There was no significant effect of PGE₂ on pluripotent stem cell levels or on the longevity of the cultures. It is concluded that excessive monopoiesis in bone marrow may be limited by PGE₂ without influencing either stem cell maintenance or the development of other marrow-derived cell types.     

Interleukin-1 inhibits PGE2 binding to macrophage-like P388D1 cells by a cyclic AMP-independent process

The interaction between interleukin IL-1α and PGE₂ on P388D₂ on cells has been investigated. Preincubation of murine macrophage-like cells, P388D₁, with IL-1α (0–73 pM) reduced the binding of PGE₂ to these cells in a concentration-dependent manner. Scatchard analysis showed that IL-1α decreased the PGE₂ binding by lowering both the high and low affinity receptor binding capacities (from 0.31 ± 0.02 to 0.12 ± 0.01 fmol/10⁶ cells for the high affinity receptor binding sites and from 2.41 ± 0.12 to 1.51 ± 0.21 fmol/10⁶ cells for the low affinity receptor binding sites). However, the dissociation constants of the receptor of the IL-1α-treated cells remained unchanged. Inhibition of PGE₂ binding IL-1α did not involve changes in either protein phosphorylation or intracellular cyclic AMP levels. Our data clearly show that IL-1α inhibits the binding of PGE₂ to monocytes/macrophages and may thereby counter the immunosuppressive actions of PGE₂.     

Prostaglandin E2 facilitates subcellular translocation of the EP4 receptor in neuroectodermal NE-4C stem cells

Prostaglandin E2 (PGE₂) is a lipid mediator released from the phospholipid membranes that mediates important physiological functions in the nervous system via activation of four EP receptors (EP1-4). There is growing evidence for the important role of the PGE₂/EP4 signaling in the nervous system. Previous studies in our lab show that the expression of the EP4 receptor is significantly higher during the neurogenesis period in the mouse. We also showed that in mouse neuroblastoma cells, the PGE₂/EP4 receptor signaling pathway plays a role in regulation of intracellular calcium via a phosphoinositide 3-kinase (PI3K)-dependent mechanism. Recent research indicates that the functional importance of the EP4 receptor depends on its subcellular localization. PGE₂-induced EP4 externalization to the plasma membrane of primary sensory neurons has been shown to play a role in the pain pathway. In the present study, we detected a novel PGE₂–dependent subcellular trafficking of the EP4 receptor in neuroectodermal (NE-4C) stem cells and differentiated NE-4C neuronal cells. We show that PGE₂ induces EP4 externalization from the Golgi apparatus to the plasma membrane in NE-4C stem cells. We also show that the EP4 receptors translocate to growth cones of differentiating NE-4C neuronal cells and that a higher level of PGE₂ enhances its growth cone localization. These results demonstrate that the EP4 receptor relocation to the plasma membrane and growth cones in NE-4C cells is PGE₂ dependent. Thus, the functional role of the PGE₂/EP4 pathway in the developing nervous system may depend on the subcellular localization of the EP4 receptor.     

Curcumin Ameliorates the Reduction Effect of PGE2 on Fibrillar β-Amyloid Peptide (1-42)-Induced Microglial Phagocytosis through the Inhibition of EP2-PKA Signaling in N9 Microglial Cells

Inflammatory activation of microglia and β amyloid (Aβ) deposition are considered to work both independently and synergistically to contribute to the increased risk of Alzheimer’s disease (AD). Recent studies indicate that long-term use of phenolic compounds provides protection against AD, primarily due to their anti-inflammatory actions. We previously suggested that phenolic compound curcumin ameliorated phagocytosis possibly through its anti-inflammatory effects rather than direct regulation of phagocytic function in electromagnetic field-exposed N9 microglial cells (N9 cells). Here, we explored the prostaglandin-E₂ (PGE₂)-related signaling pathway that involved in curcumin-mediated phagocytosis in fibrillar β-amyloid peptide (1–42) (fAβ₄₂)-stimulated N9 cells. Treatment with fAβ₄₂ increased phagocytosis of fluorescent-labeled latex beads in N9 cells. This increase was attenuated in a dose-dependent manner by endogenous and exogenous PGE₂, as well as a selective EP2 or protein kinase A (PKA) agonist, but not by an EP4 agonist. We also found that an antagonist of EP2, but not EP4, abolished the reduction effect of PGE₂ on fAβ₄₂-induced microglial phagocytosis. Additionally, the increased expression of endogenous PGE₂, EP2, and cyclic adenosine monophosphate (AMP), and activation of vasodilator-stimulated phosphoprotein, cyclic AMP responsive element-binding protein, and PKA were depressed by curcumin administration. This reduction led to the amelioration of the phagocytic abilities of PGE₂-stimulated N9 cells. Taken together, these data suggested that curcumin restored the attenuating effect of PGE₂ on fAβ₄₂-induced microglial phagocytosis via a signaling mechanism involving EP2 and PKA. Moreover, due to its immune modulatory effects, curcumin may be a promising pharmacological candidate for neurodegenerative diseases.     

Differential Effects of Prostaglandin E1 and Prostaglandin E2 on Growth and Differentiation of Murine Myeloid Leukemic Cell Line,M1

Effects of prostaglandins (PGs) of the E series on growth and differentiation of murine myeloid leukemic cell line M1 were studied. PGE₁, but not PGE₂, inhibited the growth of M1 cells. PGE₂ neither inhibited nor augmented the antiproliferative effect of PGE₁. PGE₁ augmented the differentiation of M1 cells into macrophage-like cells induced by interleukin 6. PGE₂, however, did not exhibit any effect on the differentiation. PGE₁ caused a marked increase in intracellular cAMP level in M1 cells, whereas PGE₂ had no effect. These results indicate that M1 cells are able to respond only to PGE₁. Radiolabeled PGE₁ binding experiments, however, revealed that there was no specific binding in M1 cells, suggesting that the cells express low numbers of receptors or very low affinity receptors specific for PGE₁. Stable agonists of PGI₂, iloprost, cicaprost or carbacyclin, also potently inhibited the growth of M1 cells. These findings suggest that PGE₁ as well as PGI₂ may play a role in the differentiation of monocyte-macrophage lineage cells.     

Suppression of Interleukin-11–mediated bone resorption by cyclooxygenases inhibitors

We previously found that human melanoma (A375M) and human breast cancer (MDA-MB-231) cells formed osteolytic bone metastasis in vivo. These cancer cells produced interleukin-11 (IL-11) by themselves and stimulated its production from osteoblasts. Interleukin-11 could increase the number of osteoclasts and raise the calcium concentration in the medium of neonatal murine calvaria organ culture, indicating bone resorption in vitro. Therefore, IL-11 could play an important role in the promotion of osteolysis at the site of bone metastasis. In the present study, we used the calvaria culture system to try to clarify the mechanisms of IL-11–mediated bone resorption. The murine calvaria expressed both the specificity-determining α subunit and the signal–transducing β subunit (gp130) of the IL-11 receptor. When IL-11 was added to the calvaria culture, the concentrations of prostaglandin E₂ (PGE₂) was elevated. Pretreatment of calvaria with cyclooxygenases inhibitors (e.g., indomethacin, NS-398, and dexamethasone) suppressed the production of PGE₂ and the bone resorption induced by IL-11. Addition of exogenous PGE₂ overcame the inhibitory effect of cyclooxygenases inhibitors and promoted bone resorption. These results indicate that IL-11 promotes bone resorption through a PGE₂ synthesis–dependent mechanism and that cyclooxygenases inhibitors could be interesting drugs to suppress IL-11–mediated osteolytic bone metastasis of cancer cells. J. Cell. Physiol. 175:247–254, 1998. © 1998 Wiley-Liss, Inc.     

Coexpression of osteogenic and adipogenic differentiation markers in selected subpopulations of primary human mesenchymal progenitor cells

Knowledge of the basic mechanisms controlling osteogenesis and adipogenesis might provide new insights into the prevention of osteoporosis and age-related osteopenia. With the help of magnetic cell sorting and fluorescence activated cell sorting (FACS), osteoblastic subpopulations of mesenchymal progenitor cells were characterized. Alkaline phosphatase (AP) negative cells expressed low levels of osteoblastic and adipocytic markers. AP positive cells expressed adipocytic markers more strongly than the AP negative cell populations, thus suggesting that committed osteoblasts exhibit a greater adipogenic potential. AP negative cells differentiated to the mature osteoblastic phenotype, as demonstrated by increased AP-activity and osteocalcin secretion under standard osteogenic culture conditions. Surprisingly, this was accompanied by increased expression of adipocytic gene markers such as peroxisome proliferator-activated receptor-gamma2, lipoprotein lipase and fatty acid binding protein. The induction of adipogenic markers was suppressed by transforming growth factor-beta1 (TGF-beta1) and promoted by bone morphogenetic protein 2 (BMP-2). Osteogenic culture conditions including BMP-2 induced both the formation of mineralized nodules and cytoplasmic lipid vacuoles. Upon immunogold electron microscopic analysis, osteoblastic and adipogenic marker proteins were detectable in the same cell. Our results suggest that osteogenic and adipogenic differentiation in human mesenchymal progenitor cells might not be exclusively reciprocal, but rather, a parallel event until late during osteoblast development.     

Inhibition of chondrogenesis by retinoic acid in limb mesenchymal cells in vitro: Effects on PGE2 and cyclic AMP concentrations

Effects of retinoic acid (RA) on prostaglandin E₂ (PGE₂) and cyclic AMP (cAMP) concentrations were investigated in high density, micromass cultures of mesenchymal cells derived from chick limb buds. Exposure of cells during the initial 24 h of culture to RA concentrations between 0.05–1.0 μg/ml inhibited chondrogenesis in a dose-dependent manner with 1.0 μg/ml totally inhibiting cartilage formation. Concentrations of PGE₂ and cAMP increased during the prechondrogenic period in control cells in a closely related way and remained elevated throughout the six-day period examined. Addition of RA (0.05 and 0.5 μg/ml) did not significantly alter cAMP concentrations at any time point, but significantly elevated PGE₂ levels relative to control cells in six-day cultures in a concentration-dependent manner. Addition of dibutyryl cAMP enhanced chondrogenesis in control cells between days 3 and 4, but failed to alter the inhibitory effect of RA on chondrogenesis. The results indicate that while PGE₂ and cAMP are important signals in cartilage differentiation, the inhibitory effects of RA on this process are mediated through some other mechanism.     

24,25-(OH)2D3 regulates protein kinase C through two distinct phospholipid-dependent mechanisms

We have previously shown that 24,25-(OH)₂D₃ plays a major role in resting zone (RC) chondrocyte differentiation and that this vitamin D metabolite regulates protein kinase C (PKC). The aim of the present study was to identify the signal transduction pathway used by 24,25-(OH)₂D₃ to stimulate PKC activation. Confluent, fourth passage RC cells from rat costochondral cartilage were used to evaluate the mechanism of PKC activation. Treatment of RC cultures with 24,25-(OH)₂D₃ for 90 min produced a dose-dependent increase in diacylglycerol (DAG). Addition of R59022, a diacylglycerol kinase inhibitor, significantly increased PKC activity in cultures treated with 24,25-(OH)₂D₃. Addition of dioctanoylglycerol (DOG) to plasma membranes isolated from RC increased PKC activity 447-fold. Addition of pertussis toxin or cholera toxin to control cultures elevated basal PKC activity. When added together with 10⁻⁹ M 24,25-(OH)₂D₃, there was an additive effect on PKC activity but in cultures treated with 10⁻⁸ M 24,25-(OH)₂D₃, only the hormone-dependent stimulation of PKC was observed. The phospholipase C inhibitor, U73-122, had no effect on PKC activity, indicating that the DAG produced in response to 24,25-(OH)₂D₃ is not derived from phosphatidylinositol. Addition of the tyrosine kinase inhibitor, genistein, also had no effect on 24,25-(OH)₂D₃-stimulated PKC, further supporting the hypothesis that phospholipase C is not involved in the mechanism and that phospholipase D is responsible for the increase in DAG production. Phospholipase A₂ inhibitors, quinacrine and AACOCF3, and the cyclooxygenase inhibitor indomethacin increased PKC activity in the RC cultures. Exogenous PGE₂, one of the downstream products of phospholipase A₂ action, inhibited PKC activity. These results suggest that 24,25-(OH)₂D₃ regulates PKC activity by two distinct phospholipid-dependent mechanisms: production of DAG via phospholipase D and inhibition of the production of PGE₂ via inhibition of phospholipase A₂ and cyclooxygenase. © 1996 Wiley-Liss, Inc.     

Estrogen metabolites in the release of inflammatory mediators from human amnion-derived cells

AimsHuman amnion-derived cells have been used as in vitro models to test the release of inflammatory mediators, such as arachidonic acid (AA) and prostaglandin E₂ (PGE₂). We compared estrogen metabolites for their ability to induce AA release, to influence PGE₂ production and to interact toward intracellular estrogen receptors (ERs).Main methodsMetabolite effects on AA and PGE₂ release were examined by radiolabelled substrate incorporation and by colorimetric enzyme immunoassays, respectively. [³H]17-β-estradiol binding displacements were performed on Ro-20-1724 treated whole cells.Key findingsIn WISH cells, estrone, 2-hydroxy-estrone and estriol induced a rapid dose dependent release of AA that was not inhibited by cycloheximide. Estrone and 2-hydroxy-estrone showed biphasic dose–response curves of PGE₂, whereas estriol and 16-α-hydroxy-estrone increased PGE₂ levels at high concentrations. 2-methoxy-estrone, 4-hydroxy-estradiol and 4-hydroxy-estrone did not significantly affect PGE₂ release. 2-methoxy-estradiol and 2-hydroxy-estradiol decreased the PGE₂ release. Effects of metabolites on PGE₂ were inhibited by cycloheximide and by the ER antagonist tamoxifen. In AV3 cells PGE₂ production was poorly detectable. On Ro-20-1724 treated WISH cells the K_i of 17-β-estradiol was 29.2 ± 5.4 nM. Estrone, 2-methoxy-estrone and 2-methoxy-estradiol showed similar affinity values. The hydroxyl substituent at position 2, 4 and 16 decreased or markedly increased the affinity for estradiol or estrone derivatives, respectively.SignificanceThe estrogen metabolites induced nongenomic effects on AA release from WISH cells. The influence on PGE₂ release was detectable only on WISH cells. These effects appeared genomic and mediated by intracellular ERs, whose properties seemed strongly dependent on intracellular cAMP levels.