Stimulation of human chondrocyte prostaglandin E2 production by recombinant human interleukin-1 and tumour necrosis factor

In this study we have examined the effects of recombinant cytokine preparations on the production of prostaglandin E2 (PGE2) by human articular chondrocytes in both chondrocyte monolayer and cartilage organ cultures. The cytokines chosen for this study included only those reported to be present in rheumatoid synovial fluids and which therefore could conceivably play a role in chondrocyte activation in inflammatory arthritis. Of the cytokines tested, interleukin-1 (IL-1; alpha and beta forms) consistently induced the highest levels of PGE2 production followed, to a lesser extent, by tumour necrosis factor (TNF; alpha and beta forms). The IL-1s were effective at concentrations 2-3 orders of magnitude less than the TNFs, with each cytokine demonstrating a dose-dependent increase in PGE2 synthesis for the two culture procedures. The increased PGE2 production by the chondrocytes exhibited a lag phase of 4-8 h following the addition of the IL-1 or TNF and was inhibited by actinomycin D and cycloheximide, indicating a requirement for de novo RNA and protein synthesis, respectively. Our results suggest that IL-1 may be the key cytokine involved in modulating chondrocyte PGE2 production in inflammatory arthritis; they further extend the list of human chondrocyte responses which are affected by both IL-1 and TNF.     

Stimulation of bone formation by prostaglandin E2

We examined the effect of prostaglandin E2 (PGE2), in the presence or absence of cortisol, on bone formation in 21-day fetal rat calvaria maintained in organ culture for 24 to 96 h. [3H]Thymidine and [3H] proline incorporation were used to assess DNA and collagen synthesis, respectively. Changes in dry weight and DNA content were assessed after 96 h. PGE2 (10(-7) M) stimulated both DNA and collagen synthesis in calvaria. The effect on DNA synthesis was early (24 h), transient and limited to the periosteum. Collagen synthesis was stimulated at a later time (96 h), predominantly in the central bone. Cortisol (10(-7) M) inhibited DNA and collagen synthesis. The addition of PGE2 reversed the inhibitory effects of cortisol on DNA synthesis and content and increased collagen synthesis in central bone to levels above control untreated cultures. We conclude that PGE2 has stimulatory effects on bone formation and can reverse the inhibitory effects of cortisol. Hence the effects of cortisol may be mediated in part by their ability to reduce the endogenous production of prostaglandins.     

Actions of recombinant interleukin 1, interleukin 2, and interferon-gamma on bone resorption in vitro

Human peripheral blood cells, when cultured in vitro, release bone-resorbing factors, which have been called osteoclast-activating factors (OAF) but remain unidentified. We showed previously that a monocyte product, similar to interleukin 1 (IL 1), is a powerful stimulator of bone resorption in vitro. However, the possibility remained that other immune cell products may contribute to OAF activity. We have therefore tested three recombinant cytokines; IL 1, interleukin 2 (IL 2), and interferon-gamma (IFN-gamma) for their activity in a neonatal mouse bone resorption assay. We report here that purified recombinant murine IL 1 is a potent and powerful stimulator of bone resorption in vitro, active over a concentration range of 0.14 to 33 U/ml (1.3 X 10(-12) to 3.1 X 10(-10) M). IL 1-stimulated bone resorption was unaffected by cyclooxygenase inhibition but was inhibited by calcitonin and IFN-gamma. IL 2 had no effect on bone resorption.     

Gamma interferon inhibits basal and interleukin 1-induced prostaglandin production and bone resorption in neonatal mouse calvaria

Production of the osteolytic arachidonic acid metabolites, prostaglandin (PG) E2, PGI2 and PGF2 alpha, by neonatal mouse calvariae was quantitated by gas chromatography/mass spectrometry. Mouse recombinant interleukin 1 (rIL-1) raised medium levels of PGE2 and PGI2 (measured as 6-keto-PGF1 alpha) in the dose range tested (1.0-10.0 U/ml culture medium), while an effect on PGF2 was only observed at 10 U/ml. Bone resorption in response to rIL-1 reached a plateau at 3.0 U/ml. Mouse recombinant gamma-interferon (rIFN-gamma) between 100-500 U/ml suppressed basal PG synthesis and spontaneous resorption of cultured bone. In addition, IFN-gamma at 100 U/ml prevented stimulation of PG synthesis by 3.0 U/ml rIL-1 and thereby reduced the bone resorbing activity of the cytokine by at least 60%. 5 X 10(-7) M indomethacin was equally effective in suppression of PG synthesis and bone resorption. The present study provides evidence that IFN-gamma inhibits PG synthesis and consequently resorption of cultured bone.     

Impaired bone resorption to prostaglandin E2 in prostaglandin E receptor EP4-knockout mice

Prostaglandin E(2) (PGE(2)) acts as a potent stimulator of bone resorption. In this study, we first clarified in normal ddy mice the involvement of protein kinase A and induction of matrix metalloproteinases (MMPs) in PGE(2)-induced bone resorption, and then identified PGE receptor subtype(s) mediating this PGE(2) action using mice lacking each subtype (EP1, EP2, EP3, and EP4) of PGE receptor. In calvarial culture obtained from normal ddy mice, both PGE(2) and dibutyryl cyclic AMP (Bt(2)cAMP) stimulated bone resorption and induced MMPs including MMP-2 and MMP-13. Addition of an inhibitor of protein kinase A, H89, or an inhibitor of MMPs, BB94, significantly suppressed bone-resorbing activity induced by PGE(2.) In calvarial culture from EP1-, EP2-, and EP3-knockout mice, PGE(2) stimulated bone resorption to an extent similar to that found in calvaria from the wild-type mice. On the other hand, a marked reduction in bone resorption to PGE(2) was found in the calvarial culture from EP4-knockout mice. The impaired bone resorption to PGE(2) was also detected in long bone cultures from EP4-knockout mice. Bt(2)cAMP greatly stimulated bone resorption similarly in both wild-type and EP4-knockout mice. Induction of MMP-2 and MMP-13 by PGE(2) was greatly impaired in calvarial culture from EP4-knockout mice, but Bt(2)cAMP stimulated MMPs induction similarly in the wild-type and EP4-knockout mice. These findings suggest that PGE(2) stimulates bone resorption by a cAMP-dependent mechanism via the EP4 receptor.     

Contribution of membrane-associated prostaglandin E2 synthase to bone resorption

This study initially confirmed that, among prostaglandins (PGs) produced in bone, only PGE(2) has the potency to stimulate osteoclastogenesis and bone resorption in the mouse coculture system of osteoblasts and bone marrow cells. For the PGE(2) biosynthesis two isoforms of the terminal and specific enzymes, membrane-associated PGE(2) synthase (mPGES) and cytosolic PGES (cPGES) have recently been identified. In cultured mouse primary osteoblasts, both mPGES and cyclooxygenase-2 were induced by the bone resorptive cytokines interleukin-1, tumor necrosis factor-alpha, and fibroblast growth factor-2. Induction of mPGES was also seen in the mouse long bone and bone marrow in vivo by intraperitoneal injection of lipopolysaccharide. In contrast, cPGES was expressed constitutively both in vitro and in vivo without being affected by these stimuli. An antisense oligonucleotide blocking mPGES expression inhibited not only PGE(2) production, but also osteoclastogenesis and bone resorption stimulated by the cytokines, which was reversed by addition of exogenous PGE(2). We therefore conclude that mPGES, which is induced by and mediates the effects of bone resorptive stimuli, may make a target molecule for the treatment of bone resorptive disorders.     

alpha-Lipoic acid inhibits inflammatory bone resorption by suppressing prostaglandin E2 synthesis

alpha-Lipoic acid (LA) has been intensely investigated as a therapeutic agent for several pathological conditions, including diabetic polyneuropathy. In the present study, we examined the effects of LA on osteoclastic bone loss associated with inflammation. LA significantly inhibited IL-1-induced osteoclast formation in cocultures of mouse osteoblasts and bone marrow cells, but LA had only a marginal effect on osteoclastogenesis from bone marrow macrophages induced by receptor activator of NF-kappaB ligand (RANKL). LA inhibited both the sustained up-regulation of RANKL expression and the production of PGE2 induced by IL-1 in osteoblasts. In addition, treatment with either prostaglandin E2 (PGE2) or RANKL rescued IL-1-induced osteoclast formation inhibited by LA or NS398, a specific cyclooxygenase-2 (COX-2) inhibitor, in cocultures. LA blocked IL-1-induced PGE2 production even in the presence of arachidonic acid, without affecting the expression of COX-2 and membrane-bound PGE2 synthase. Dihydrolipoic acid (the reduced form of LA), but not LA, attenuated recombinant COX-2 activity in vitro. LA also inhibited osteoclast formation and bone loss induced by IL-1 and LPS in mice. Our results suggest that the reduced form of LA inhibits COX-2 activity, PGE2 production, and sustained RANKL expression, thereby inhibiting osteoclast formation and bone loss in inflammatory conditions.     

The activation of human fibroblast prostaglandin E production by interleukin 1

We have examined the induction of prostaglandin E2 (PGE2) release from fibroblasts by human interleukin 1 (IL-1). A number of fibroblast cell lines appear to respond to IL-1 in a fashion similar to that seen with synovial fibroblast cultures. Using the Gin-1 primary fibroblast cell line, the earliest time where a significant increase in PGE2 release can be detected is 2 hr. Thereafter PGE2 appears to increase dramatically, with levels after 5 hr increased over 50-fold above baseline. IL-1 appears to directly induce the increase in PGE2 since removal of other proteins from culture medium does not affect induction. PGE2 induction by IL-1 also does not require cell proliferation. The induction appears to involve the synthesis of new protein since the enhanced release can be completely blocked by addition of actinomycin D or cycloheximide. Arachidonic acid mobilization in cells does not appear to be altered following IL-1 addition. However, the ability to convert arachidonic acid to PGE2 is increased following 5 hr of culture with IL-1. While increasing the release of PGE2, the addition of phorbol esters, alone or in combination with calcium ionophores, does not mimic the protein synthesis-dependent increase seen with IL-1. Taken together these results suggest that IL-1 induction of fibroblast PGE2 involves the synthesis of new protein or proteins involved in the conversion of free arachidonic acid to PGE2.     

Effects of prostaglandin E2 on macrophages and osteoclasts in cultured fetal long bones

Summary Bone cultures exposed to prostaglandin E₂ (PGE₂) revealed an increase in ⁴⁵Ca release from bone to medium and an increase in osteoclast number compared to control bones. In addition, PGE₂-treated osteoclasts contained a more extensive ruffled border region than control osteoclasts. These data suggest that PGE₂ activates existing osteoclasts and causes proliferation and differentiation of osteoclast precursor cells. The existence of macrophages in resorbing fetal bone explants was documented. These macrophages contain numerous phagolysosomes and lipid vacuoles and are often located adjacent to osteoclasts or closely apposed to calcified tissue surfaces. PGE₂ caused an early increase in the number of macrophages. It is postulated that fetal bone macrophages are primarily engaged in phagocytosis and digestion of cellular debris, but also play a role in the process of bone resorption.This study was supported by Grant DE-04443 from USPHS     

Natural and recombinant human IL-1 receptor antagonists block the effects of IL-1 on bone resorption and prostaglandin production

Inhibitory factors towards IL-1 have been identified in the urine and in the supernatants of human monocyte cultures and have been shown to act as receptor antagonists. We have investigated whether a natural inhibitor purified from human urine (uIL-1ra) and a recombinant molecule expressed using the gene for an IL-1 antagonist isolated from monocytes (rIL-1ra) can alter responses to human rIL-1 alpha in organ cultures of fetal rat long bones and neonatal mouse calvariae. The two preparations probably contained similar or identical molecules, because an antibody to rIL-1ra reacted with uIL-1ra by Western blot analysis. uIL-1ra and rIL-1ra specifically blocked stimulation of bone resorption by rIL-1 in both culture systems, as well as the increase in PGE2 production in cultured calvariae. Resorptive effects of parathyroid hormone and TNF-alpha were not blocked. The uIL-1ra preparation had some intrinsic resorbing activity, but on gel chromatography this appeared in fractions that eluted earlier than uIL-1ra. Concentration ratios of rIL-1ra to rIL-1 as low as 10 could block the resorptive response of fetal rat long bones, whereas concentration ratios of 100 to 1000 were required to block IL-1 action on neonatal mouse calvariae. The inhibitory effects appeared to be competitive, because increasing concentrations of IL-1 overcame the block of bone resorption in both systems and the inhibition of PGE2 production in calvariae.     

Recombinant human interleukin 1 alpha and beta stimulate mouse osteoblast-like cells (MC3T3-E1) to produce macrophage-colony stimulating activity and prostaglandin E2

The effects of interleukin 1 (IL-1) on MC3T3-E1 cells (clonal osteoblast-like cells established from mouse calvaria) were studied to elucidate the mechanism of IL-1-induced bone resorption. Recombinant human interleukin 1 alpha (rhIL-1 alpha) and beta (rhIL-1 beta) stimulated PGE2 production in MC3T3-E1 cells in a dose dependent manner. rhIL-1 alpha and 1 beta also stimulated MC3T3-E1 cells to produce macrophage-colony stimulating activity (M-CSA) in a dose-dependent manner. Indomethacin completely abolished PGE2 production but did not affect CSA. These results suggest that bone resorption induced by IL-1s is at least in part mediated by PGE2 produced by osteoblasts, and that M-CSA produced by osteoblasts may synergistically potentiate bone resorption by recruiting osteoclast precursors.     

Effects of indomethacin, prostaglandin E2, prostaglandin F2 alpha and 6-keto-prostaglandin F1 alpha on hatching of mouse blastocysts

The present study has been performed to investigate how PGs would participate the hatching process. Effects of indomethacin, an antagonist to PGs biosynthesis, on the hatching of mouse blastocysts were examined in vitro. Furthermore, it was studied that prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) or 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were added to the culture media with indomethacin. The hatching was inhibited by indomethacin yet the inhibition was reversible. In the groups with indomethacin and PGE2, no improvement was seen in the inhibition of hatching and the inhibition was irreversible. In the groups with indomethacin and PGF2 alpha, inhibition of hatching was improved in comparison with the group with indomethacin. In the groups with indomethacin and 6-keto-PGF1 alpha, no improvement was seen. The above results indicated that PGF2 alpha possibly had an accelerating effect on hatching and a high concentration of PGE2 would exert cytotoxic effect on blastocysts.     

Continuously applied compressive pressure induces bone resorption by a mechanism involving prostaglandin E2 synthesis

In previous research, we devised a specific culture chamber to examine the effect of continuously applied compressive pressure (CCP) on bone formation and resorption. The chamber was infused with compressed mixed gases with different O2 and CO2 composition to maintain the pO2, pCO2, and pH in the culture medium under pressures of +0.5 atm (1.5 atm total) to +2.0 atm (3.0 atm total) at the same levels as those at the ordinary pressure (1 atm). Using the specific culture chamber, we demonstrated that CCP greatly suppressed the differentiation of mouse osteoblast-like MC3T3-E1 cells. The inhibition by CCP appeared to be mediated by prostaglandin E2 (PGE2). In the present study, we examined the effect of CCP on osteoclastic bone resorption. CCP treatment of mouse bone marrow culture markedly increased both the PGE2 production and the number of tartrate-resistant acid phosphatase (TRACP)-positive mononuclear cells (possibly precursors of multinucleated osteoclasts). An autoradiographic study using [125I]-salmon calcitonin showed clearly that those TRACP-positive cells had calcitonin receptors. The CCP effect was the greatest at +1.0 atm (2.0 atm total). Isobutylmethylxanthine potentiated the production of TRACP-positive cells induced by CCP. Adding indomethacin completely inhibited both the TRACP-positive cell formation and the PGE2 production induced by CCP. CCP also increased the release of 45Ca from prelabeled mouse calvaria during later stages (2-6 days) of the 6-day culture period. CCP markedly increased PGE2 but not interleukin 1 in the culture media of mouse calvaria. These results indicate that, besides inhibiting osteoblast differentiation, CCP stimulates bone resorption by generating new osteoclasts through a mechanism involving PGE2 production.     

Induction of colony stimulating factor in vivo by recombinant interleukin 1 alpha and recombinant tumor necrosis factor alpha 1

In response to a potent inflammatory challenge, such as Gram-negative endotoxin, a number of cytokines are induced that, in turn, mediate many of the pathophysiologic alterations associated with endotoxicity. In this study, we have observed two endotoxin-associated monokines, recombinant interleukin-1 alpha (rIL 1 alpha) and recombinant tumor necrosis factor alpha (rTNF alpha), to induce colony stimulating factor (CSF) in vivo. The CSF activities produced in response to rIL 1 alpha or rTNF alpha gave rise to a mixture of granulocyte-macrophage colonies and were induced in a dose- and time-dependent fashion, peaking within 3 hr of cytokine injection (preceding peak CSF induction by endotoxin by several hours). Combined injection of suboptimal concentrations of rIL 1 alpha and rTNF alpha were additive, and simultaneous injection of optimal concentrations of each failed to increase CSF levels over that observed with either cytokine alone. Unlike endotoxin, neither cytokine induced interferon in vivo. These findings extend our understanding of the cytokine cascade that is operative in an inflammatory response and may account for many of the observed hematopoietic alterations that accompany inflammation.     

Effects of prostaglandin E2 on alveolar bone resorption during orthodontic tooth movement

Twenty Sprague-Dawley rats weighing 280-300 g were divided into two groups of ten animals each. They were treated by daily submucosal injections of 50 micrograms prostaglandin E2 (PGE2) per kilogram body weight into the region below the apex of the left first maxillary molar (experimental), or vehicle into the region below the apex of the right first molar (control), for a period of 5 days. The animals of the first group were sacrificed immediately following the treatment period, while those of the second group were sacrificed 5 days after the treatment period. Twenty-two hours prior to sacrifice, a piece of latex orthodontic elastic was secured to the adjacent area between the first and second maxillary molars of both sides of each rat by using two mosquito hemostats. The periodontal ligament (PDL) mesial to the mesiobuccal root of the first maxillary molar was assayed for changes in PDL cell factors. The results showed that immediately following the 5-day treatment period the left PDL had a significant decrease in the total number of fibroblasts and a significant increase in the total number of both osteoclasts and nuclei per osteoclast, while no significant changes in the osteoblasts when compared with those of the right control PDL. The left PDL of animals which were sacrificed 5 days after the treatment period revealed a significant decrease in the number of total fibroblasts and only a slight decrease in both numbers of total osteoclasts and total nuclei per osteoclast, but again no significant changes in osteoblasts when compared with those of the right control PDL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bradykinin synergistically potentiates interleukin-1 induced bone resorption and prostanoid biosynthesis in neonatal mouse calvarial bones

Interleukin-1 (IL-1) alpha and beta dose-dependently stimulated the release of 45Ca and the formation of prostaglandin E2 (PGE2) and PGI2 in cultured mouse calvarial bones, with IL-1 beta being the most potent agonist. Bradykinin (BK; 10 nmol/l) synergistically potentiated the effect of IL-1 alpha (10 pg/ml) and IL-1 beta (5 pg/ml) both on 45Ca release and on biosynthesis of PGE2 and PGI2. The capacity of BK to potentiate IL-1 beta induced 45Ca release and PGE2 formation was seen at concentrations of BK from 1-1000 nmol/l. These data indicate that BK and IL-1, which are formed in inflammatory processes, may act in concert to stimulate bone resorption in the vicinity of inflammatory lesions.     

Stimulation of B cell growth and differentiation by murine recombinant interleukin 1

Purified splenic B cells from C57BL/6 mice were separated into high-density (resting) and low-density (activated) B cells. Separated B cell populations were cultured at low cell densities (1 X 10(4) cells/well) with recombinant interleukin 1 (r-IL 1) alone or in combination with dextran sulfate (DXS) or anti-IgM monoclonal antibodies (alpha IgM mab), respectively, and proliferative responses were determined. R-IL 1 alone, as well as in synergy with alpha IgM mab or DXS, respectively, stimulated the growth of low-density B cells. Moreover, r-IL 1 and alpha IgM mab costimulated replication of high-density B cells. Separated B cell populations (1 X 10(5) cells/well) were cultured with r-IL 1 alone or in combination with DXS or alpha IgM mab, respectively, and the generation of plaque-forming cells was determined. R-IL 1 alone, as well as in synergy with DXS, stimulated the differentiation of low-density B cells into Ig-secreting cells. These findings suggest that r-IL 1 has B cell growth and differentiation factor activity and is operative on high- and low-density B cells. Thus, IL 1 may play an important role in B cell growth and maturation.     

Stimulation of prostaglandin E2 and thromboxane B2 production by human monocytes in response to interleukin-2

Interleukin 2 (IL-2) is a potent lymphokine involved in the regulation of immune responses and is classically regarded as a stimulus for the activation and growth of T-cells. Recent reports have demonstrated the IL-2 dependent activation of human peripheral blood lymphocytes into lymphokine activated killer cells capable of lysing tumor cells both in vitro and in vivo. In this study we report data which clearly show IL-2 may also act to down-regulate the immune response by inducing the synthesis of arachidonic acid metabolites with known immunosuppressive actions. Stimulation of peripheral human blood monocytes with IL-2 caused an increased production of prostaglandin E2 (PGE2) and thromboxane (TXB2) in a dose-dependent manner. Kinetic analysis showed no increase above controls after 6 hours and maximal levels by 10 hours; elevated levels were maintained after 45 hours of incubation. After 20 hours of stimulation with 2000 U/ml IL-2, the level of PGE2 and TXB2 were greater than three-fold above controls, 0.7 and 19 ng/10(6) cells, respectively. The stimulation was relatively specific in that neither prostacyclin nor leukotrienes were produced in response to IL-2. These data demonstrate that IL-2 acts on human monocytes to induce the secretion of PGE2 and TXB2.