Stimulation of bone resorption by various prostaglandins in organ culture

Inflammatory and immune pathways in the pathogenesis of periodontal disease

The pathogenesis of periodontitis involves a complex immune/inflammatory cascade that is initiated by the bacteria of the oral biofilm that forms naturally on the teeth. The susceptibility to periodontitis appears to be determined by the host response; specifically, the magnitude of the inflammatory response and the differential activation of immune pathways. The purpose of this review was to delineate our current knowledge of the host response in periodontitis. The role of innate immunity, the failure of acute inflammation to resolve (thus becoming chronic), the cytokine pathways that regulate the activation of acquired immunity and the cells and products of the immune system are considered. New information relating to regulation of both inflammation and the immune response will be reviewed in the context of susceptibility to, and perhaps control of, periodontitis.

Effects of prostaglandin E1 on callus formation in rabbits

BACKGROUND

Recent research has focused on identifying chemical modulators of osteogenesis. We present initial findings on the osteoinductive properties of prostaglandin Е1 (Vasaprostan), using a rabbit model.

METHODS

Data were collected on callus formation in 14 male rabbits. These were divided into two groups (control and treatment) with 7 animals in each group. In all animals, the right tibia was fractured using a standardized protocol and stabilized by an intramedullary nail. Treatment group received a 5 μg/kg subcutaneous injection of PGE1/day during 10 postoperative days. Visual and radiological evaluation of callus formation was prospectively collected. After 30 days, all animals were killed and the tibia specimens were examined histologically.

RESULTS

In all the treatment group animals, fractures were consolidated radiologically by day 30. No treatment group animals and two control group animals were excluded form the experiment. In the control group, 4 animals demonstrated slower callus formation than the main group. Two control group animals were excluded from the experiment on the 20th day due to wound infection; one developed a nonunion. The mean coefficient of bone callus thickening in the main group was 2.08 (±0, 16) and 1.77 (±0.05) (p < 0.05) in the control group. Calculation of mean quantity of neogenic vessels in 10 random visual fields of the bone callus revealed 78 (±9.82) in the main group and 40 (±4.68) in the control group (p < 0.05).

CONCLUSIONS

Our study demonstrates an increased rate and amount of bone callus formation in the group treated with prostaglandin E1 compared to the control group. Prospective radiological analysis was corroborated by histologic evaluation.

Mid- and long-term clinical results of surgical therapy in unicameral bone cysts

Background

Unicameral (or simple) bone cysts (UBC) are benign tumours most often located in long bones of children and adolescents. Pathological fractures are common, and due to high recurrence rates, these lesions remain a challenge to treat. Numerous surgical procedures have been proposed, but there is no general consensus of the ideal treatment. The aim of this investigation therefore was to study the long-term outcome after surgical treatment in UBC.

Methods

A retrospective analysis of 46 patients surgically treated for UBC was performed for short and mid-term outcome. Clinical and radiological outcome parameters were studied according to a modified Neer classification system. Long-term clinical information was retrieved via a questionnaire at a minimum follow-up of 10 years after surgery.

Results

Forty-six patients (17 female, 29 male) with a mean age of 10.0 ± 4.8 years and with histopathologically confirmed diagnosis of UBC were included. Pathological fractures were observed in 21 cases (46%). All patients underwent surgery for UBC (35 patients underwent curettage and bone grafting as a primary therapy, 4 curettage alone, 3 received corticoid instillation and 4 decompression by cannulated screws). Overall recurrence rate after the first surgical treatment was 39% (18/46), second (17.4% of all patients) and third recurrence (4.3%) were frequently observed and were addressed by revision surgery. Recurrence was significantly higher in young and in male patients as well as in active cysts. After a mean of 52 months, 40 out of 46 cysts were considered healed. Prognosis was significantly better when recurrence was observed later than 30 months after therapy. After a mean follow-up of 15.5 ± 6.2 years, 40 patients acknowledged clinically excellent results, while five reported mild and casual pain. Only one patient reported a mild limitation of range of motion.

Conclusions

Our results suggest satisfactory overall long-term outcome for the surgical treatment of UBC, although short-and mid-term observation show a considerable rate of recurrence independent of the surgical technique.

Dental Pulp and Periodontal Ligament Cells Support Osteoclastic Differentiation

Odontoclasts and cementoclasts are considered to play major roles in the internal resorption of dentin and the external resorption of tooth roots. In this study, we evaluated the osteoclast-inducing ability of human dental pulp and periodontal ligament cells, which are mesenchymal cells in dental tissues. These cells expressed RANKL and OPG mRNA constitutively. As osteoclast precursors, CD14+ monocytes derived from human peripheral blood were isolated, and incubated together with human dental pulp or periodontal ligament cells. Both cell types spontaneously induced the differentiation of CD14+ monocytes into osteoclasts without osteotropic factors. These results suggest that dental pulp and periodontal ligament cells are involved in regulating the differentiation and function of osteoclasts.

The effect of nonsteroidal anti-inflammatory agents on spinal fusion

A large body of information suggests NSAIDS have a negative impact on the healing of bone. Although each clinical healing scenario presents a slightly different level of challenge, the healing of a posterolateral spinal fusion is one of the most difficult challenges in bony healing. Clinically, this results in a relatively high rate of nonunions using traditional fusion techniques. Spinal fusion models have confirmed NSAIDS have a definite inhibitory effect on healing of the fusion. Although data are limited, it appears this effect is most severe when NSAIDS are administered in the early postoperative period. Moreover, the effect may be worse with certain types initial inflammatory, subsequent reparative, and final remodeling phases. Because of the anti-inflammatory activity of NSAIDS, one might assume their effects would be worse when administered in the inflammatory phase. Indeed, the study by Riew et al suggests the inhibitory effects are more significant when NSAIDS are administered earlier following fusion. Other studies conducted with non-spinal models also suggest early administration of NSAIDS results in greater inhibition of bone formation (Goodman et al). Unfortunately, the length of the inflammatory phase in humans is not well known. This leaves the clinician unsure about the safe time to allow resumption of NSAID usage clinically. It appears likely NSAID use following a spinal fusion procedure will increase the rate of pseudarthrosis. The literature suggests that avoidance of NSAIDS in the postoperative period may avoid nonunion. Additionally, we propose that chronic NSAID usage should be addressed in a similar manner to cigarette smoking. While neither are absolute contraindications to elective spinal fusion, patients should be counseled to discontinue the use of NSAIDS in the peri- and postoperative period to maximize their chance for a successful fusion.

Activation of osteoblastic functions by a mediator of pain, bradykinin

We investigated the effects of bradykinin (BK) on the production of interleukin (IL)-6 and prostaglandin PGE(2), whose molecules are capable of stimulating the development of osteoclasts from their hematopoietic precursors as well as the signal transduction systems involved, in human osteoblasts (SaM-1 cells). BK receptors B1 (B1R) and B2 (B2R) were expressed in SaM-1 and osteosarcoma (SaOS-2, HOS, and MG-63) cells. Treatment of SaM-1 cells with BK increased the synthesis of both IL-6 and PGE(2) and the increase in both was blocked by HOE140 (B2R antagonist), but not by Des-Arg(9)-[Leu(8)]-BK (B1R antagonist). U-73122, a phospholipase C (PLC) inhibitor, suppressed BK-induced IL-6 and PGE(2) synthesis in SaM-1 cells. In addition, BK caused an increase in the intracellular Ca(2+) concentration ([Ca(2+)]i), which was inhibited by pretreatment with HOE140 or 2-aminoethoxydiphenyl borate (2-APB), an inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) blocker. Furthermore, both SB203580 (an inhibitor of p38 mitogen-activated protein kinase [MAPK]) and PD98059 (an inhibitor of MEK, upstream of ERK) attenuated the BK-induced IL-6 and PGE(2) synthesis. BK treatment resulted in the phosphorylation of p38 MAPK and extracellular signal-regulated kinase (ERK)1/2, and 2-APB could suppress BK-induced phosphorylation of ERK1/2. These findings suggest that BK increased both IL-6 and PGE(2) synthesis in osteoblastic cells via B2R and that PLC, IP(3)-induced [Ca(2+)]i, MEK, and MAPKs were involved in the signal transduction in these cells.

Basic calcium phosphate crystal-induced prostaglandin E2 production in human fibroblasts: Role of cyclooxygenase 1, cyclooxygenase 2, and interleukin-1?

OBJECTIVE

To elucidate the mechanism of basic calcium phosphate (BCP) crystal-induced prostaglandin E(2) (PGE(2)) production in human foreskin fibroblasts (HFFs), to identify the signaling pathway involved in the induction of cyclooxygenase 2 (COX-2) messenger RNA (mRNA) by BCP crystals, to examine the effect of BCP crystals on interleukin-1beta (IL-1beta) mRNA expression, and to investigate the potential of phosphocitrate to abrogate the BCP crystal-induced effects.

METHODS

PGE(2) levels were quantified using a commercial enzyme immunoassay kit. COX-2 and COX-1 transcript levels were quantified using real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Induction of IL-1beta and COX-2 mRNA was examined by end-point RT-PCR. COX-2 protein expression was assessed by Western blotting.

RESULTS

PGE(2) production measured 4 and 30 hours after BCP crystal treatment was higher in BCP crystal-treated (mean +/- SEM 1,891 +/- 273 pg/microg and 1,792 +/- 233 pg/microg, respectively) than in untreated (88 +/- 5 pg/microg and 205 +/- 93 pg/microg, respectively) HFFs. The PGE(2) produced after 4 hours was sensitive to inhibition with NS398, a selective COX-2 inhibitor, implying that it was COX-2 mediated, whereas the PGE(2) produced at 30 hours could not be completely inhibited by NS398. Real-time RT-PCR demonstrated a 23-fold increase in COX-2 mRNA that was maximal at 4 hours, whereas analysis of mRNA for COX-1 showed up-regulation of transcript peaking at 24 hours poststimulation (1.75-fold increase). The protein kinase C and phosphatidylinositol 3-kinase signal-transduction inhibitors bisindolylmaleimide I and LY294002, respectively, blocked BCP crystal-induced COX-2 mRNA in HFFs. In addition, BCP crystals were found to up-regulate the proinflammatory cytokine IL-1beta (maximal at 8 hours). The induction of both COX-2 and IL-1beta by BCP crystals was attenuated when the cells were treated with phosphocitrate.

CONCLUSION

These findings indicate that BCP crystals may be an important amplifier of PGE(2) production through induction of the COX enzymes and the proinflammatory cytokine IL-1beta.

The mechanisms of the inhibitory effects of nonsteroidal anti-inflammatory drugs on bone healing: a concise review

Nonsteroidal anti-inflammatory drug (NSAID) use continues to expand at a remarkable rate due both to the broad spectrum of clinical applications for these medications and to the relatively recent introduction of the popular COX-2-selective inhibitors. The use of NSAIDs is particularly prevalent in patients with a variety of musculoskeletal conditions and injuries. Reports of impaired bone healing associated with NSAID use, therefore, are a particular cause for concern. Animal and in vitro studies have demonstrated impaired bone healing in the presence of traditional NSAIDs, as measured by a variety of different parameters. More recently, initial studies investigating the effects of COX-2-selective inhibitors on bone healing have yielded similar results. With mounting evidence that NSAIDs do in fact interfere with proper bone healing in various animal models, questions have arisen regarding the potential mechanism through which NSAIDs produce this outcome and whether these results can be translated to clinical settings. A likely pathway for these observed effects results from an understanding of the steps involved in bone healing itself. These steps include an inflammatory response, bone resorption, and new bone formation. Investigations over the past several decades have elucidated a role for prostaglandins (PGs) in each of these areas. Specifically, PGs have been shown to elicit and participate in inflammatory responses, increase osteoclast activity and subsequent bone resorption, and increase osteoblast activity and new bone formation. This apparent integral role for PGs in the process of bone healing, coupled with the knowledge that NSAIDs act by inhibiting the production of PGs, results in an understanding of the likely mechanism through which NSAIDs impart their deleterious effects on bone healing. By inhibiting the COX enzymes and the subsequent production of PGs, NSAIDs not only achieve their desired anti-inflammatory effects but also inhibit the increased production of PGs that is necessary for bone healing to occur. Despite this understanding of the potential mechanism through which NSAIDs inhibit bone healing in a laboratory setting, few studies exist that show whether these inhibitory effects are also evident clinically. Thus, further studies will need to decipher whether similar inhibitory effects occur in a clinical setting.

Milwaukee shoulder: correlating possible etiologic variables

The current study evaluated the relative correlation of apatite crystal-induced inflammation and rotator cuff deficiency in the development of cuff tear arthropathy. Thirty-seven patients with full thickness rotator cuff tears were evaluated by history, physical examination, and plain radiographs. Thirty patients had surgical intervention for their rotator cuff defects, and calipers were used intraoperatively to quantify the size of the tear in its largest diameter. The remaining seven patients were treated nonoperatively and the size of the tear was quantified using magnetic resonance imaging. Synovial fluid was obtained from all patients and analyzed for crystal content using an alizarin red stain. Synovial fluid also was analyzed for leukocyte count and differential, prostaglandin E, and matrix metalloproteinase. An unpaired Student's t test revealed that significantly higher levels of prostaglandin E were found in the synovial fluid of patients with apatite crystals, shown by alizarin red stain. Chi squared analysis showed that patients with elevated crystal levels were significantly more likely to have large rotator cuff tears or glenohumeral arthritis. Establishing such relations potentially can elucidate the etiology and treatment of this complex disorder.(2) (2)

Effect of misoprostol, a prostaglandin E1 analog, on orthodontic tooth movement in rats

The purpose of this study was to investigate the effects of oral administration of misoprostol, a prostaglandin E1 analog, on orthodontic tooth movement and root resorption in rats. Sixty-four male Sprague-Dawley rats that initially weighed 250 +/- 20 g were used in this study. The animals were randomly assigned to 1 of 6 experimental and 2 control (nonappliance and appliance) groups. The experimental groups received 2.5, 5.0, 10.0, 25.0, 50.0, and 100.0 microg/kg misoprostol by gastric lavage every 24 hours for 2 weeks. A fixed orthodontic appliance consisting of a nickel-titanium closed-coil spring, 5.0 mm long was ligated between the maxillary right incisor and the maxillary right first molar. The initial activating force was 60 g. For analysis of root resorption, 99 maxillary right and left first molars from 61 animals were chosen. Serial histologic sections of the mesial root of the maxillary first molars were made, and histologic analysis of root resorption on the mesial and distal surfaces was performed. The results showed that oral misoprostol did increase the amount of orthodontic tooth movement in all the experimental groups compared with the appliance control group. This increase was statistically significant in doses of 10.0, 25.0, 50.0, and 100.0 microg/kg (P <.001). However, there were no statistically significant differences among these 4 different doses. There were no statistically significant differences in the amount of root resorption among the groups. However, a trend toward more root resorption was registered. On the basis of these findings, oral misoprostol can be used to enhance orthodontic tooth movement with minimal root resorption.

Pharmacological studies of diacerein in animal models of inflammation, arthritis and bone resorption

Diacerein has proved to be effective in the treatment of osteoarthritis. We investigated the effects of diacerein in animal models of carrageenin-, zymosan-, or dextran-induced paw edema and adjuvant-induced arthritis and in ovariectomized rats. In acute inflammatory models, unlike classical nonsteroidal anti-inflammatory drugs such as naproxen and ibuprofen, diacerein inhibited the rat paw edema induced by various agents. In the adjuvant-induced arthritic rats, diacerein at 100 mg/kg/day significantly suppressed the paw edema and the increase in serum mucoprotein. Addition of 3 mg/kg/day naproxen to each diacerein (3, 10, 30 mg/kg/day) dose resulted in significantly greater anti-inflammatory activity than with naproxen alone. In the ovariectomized rats, diacerein (10, 100 mg/kg/day) also significantly prevented bone loss and reduced the serum alkaline phosphatase and decreased the excretion of urinary hydroxyproline. In addition, rhein (10, 30 microM) inhibited calcium release from mouse calvaria induced by interleukin-1 beta, prostaglandin E(2) and parathyroid hormone 1-34 human fragment. These findings indicate that diacerein is a novel anti-inflammatory drug with pharmacological properties different from those of classical nonsteroidal anti-inflammatory drugs and support the clinical investigation of the use of combination therapy with diacerein and nonsteroidal anti-inflammatory drugs in patients with not only osteoarthritis but also rheumatoid arthritis.

Therapeutic uses of non-steroidal anti-inflammatory drugs in dentistry

The non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely used classes of drugs for the management of acute and chronic pain in dentistry. Their therapeutic efficacy and toxicity are well-documented and provide evidence that NSAIDs generally provide an acceptable therapeutic ratio of pain relief with fewer adverse effects than the opioid-mild analgesic combination drugs that they have largely replaced for most dental applications. The great many studies done with the oral surgery model of acute pain indicate that a single dose of an NSAID is more effective than combinations of aspirin or acetaminophen plus an opioid, with fewer side-effects, thus making it preferable for ambulatory patients. The combination of an NSAID with an opioid generally results in marginal analgesic activity but with an increased incidence of side-effects, which limits its use to patients in whom the NSAID alone results in inadequate analgesia. The selective COX-2 inhibitors hold promise for clinical efficacy with less toxicity from chronic administration and may prove advantageous for the relief of chronic orofacial pain. The use of repeated doses of NSAIDs for chronic orofacial pain should be re-evaluated in light of a lack of documented efficacy and the potential for serious gastrointestinal and renal toxicity with repeated dosing.

Cyclooxygenase-2 inhibitor for pain management in osteoid osteoma

Thirteen patients with osteoid osteoma were enrolled in a prospective trial to test whether rofecoxib, a selective cyclooxygenase-2 inhibitor, is as effective for pain control as acetylsalicylic acid. Each patient documented the pain level using a visual analog scale, with 0 being no pain and 10 being unbearable pain, during 2 days of no pain medication, 4 days of 500 mg acetylsalicylic acid three times a day, and 10 days of 25 mg rofecoxib once a day. Oral administration of 500 mg acetylsalicylic acid three times a day led to a significant decrease in pain at night, pain at rest, and pain induced by exercise. Twenty-five milligrams rofecoxib given once a day at midday showed the same remarkable improvement in pain at night, pain at rest, and pain induced by exercise. Rofecoxib in comparison with acetylsalicylic acid showed a trend toward lower pain levels in all categories. Rofecoxib offered a significantly better reduction in pain at rest during the day than did acetylsalicylic acid. Results of the current study suggest that pain induction in osteoid osteoma is related to cyclooxygenase-2, an enzyme that is blocked by acetylsalicylic acid and rofecoxib. Conservative medical treatment with rofecoxib for osteoid osteoma is recommended when percutaneous intervention is associated with significant morbidity.

Biochemical responses in cultured cells following exposure to (89)SrCl(2): potential relevance to the mechanism of action in pain palliation

(89)SrCl(2) is currently used as a systemic radioactive palliative treatment for painful osseous metastases associated with an osteoblastic reaction in bone. However, the biological mechanism by which (89)SrCl(2) mediates pain palliation remains unclear. In this study, attempts were made to elucidate the mechanisms by which (89)SrCl(2) might influence pain at these sites. Both the direct radiotoxic effects of (89)SrCl(2) on cell viability and its influence on cellular biosynthetic activity were investigated. The direct radiotoxic effects of (89)SrCl(2) and X-rays were compared using the prostate carcinoma cell line, PC-3. Comparable effects upon PC-3 cell viability were seen in response to exposure to an equivalent dose given by (89)SrCl(2) and X-rays (2 Gy). Experiments to investigate the indirect action of (89)SrCl(2) exposure employed the MC3T3-E1 cell line and focused on their production of Prostaglandin E(2) (PGE(2)) and interleukin-6 (IL-6). Exposure of the MC3T3-E1 cell line to (89)SrCl(2) resulted in an increased production of PGE(2) in a concentration-dependent manner. No increased PGE(2) production was seen by the MC3T3-E1 cells in response to X-ray exposure either in the presence or absence of SrCl(2). IL-6 was produced by the MC3T3-E1 cells in response to (89)SrCl(2) exposure via a PGE(2)-mediated pathway. This study demonstrates the release of potent biochemical modifiers of bone turnover in response to the systemically applied radiotherapeutic (89)SrCl(2). This strongly suggests the mechanism of pain palliation by (89)SrCl(2) is likely to result from a complex interaction of direct and indirect radiation-induced effects.

Effects of catecholamines on calvarial bone resorption in vitro

Many important diseases in otolaryngology manifest through abnormal bone remodeling or destruction. The mechanisms for such pathological remodeling remain poorly understood. Bone is known to be innervated by norepinephrine-containing sympathetic nerves, and sympathectomy is known to induce bone resorption. The role, however, of norepinephrine as a potential bone-modulatory substance is unknown. Using the calvarial calcium release assay, we conducted the following experiment to evaluate the bone-modulatory activity of norepinephrine, the alpha-agonist octopamine, and the beta-agonist isoproterenol. Each agent was tested at 2 concentrations with and without parathyroid hormone. Norepinephrine was found to have no effect on calcium release. In contrast, octopamine at 10(-8) mol/L exerted a significant stimulatory effect on calcium release, and isoproterenol at 10(-6) mol/L exerted a significant inhibitory effect on parathyroid hormone-induced calcium release. The investigation suggests that a bimodal, concentration-dependent, receptor-specific model for catecholamine-mediated modulation of bone resorption may operate in calvarial bone.

First place--resident basic science award 1999. Effects of leukotriene and cyclo-oxygenase inhibition on adaptive bone remodeling in the middle ear

Abnormal bone remodeling is associated with important otolaryngologic diseases. In such diseases, the mechanisms of osteoclastic control underlie the pathologic processes. It is known that strain applied to auditory bullae induces bone resorption-an effect mediated by prostaglandins and blocked by cyclo-oxygenase inhibitors. It is also known that cyclo-oxygenase inhibition shunts arachidonic acid into alternate metabolic pathways, mainly the lipoxygenase pathway with leukotriene production. The role of these metabolites in adaptive bone remodeling is unknown. Using the gerbilline bulla as a model, we infused BW755c (dual lipoxygenase/cyclo-oxygenase inhibitor) and L-663,536 (5-lipoxygenase inhibitor) into animals undergoing middle ear pressurization. After 7 days, the bulla bones were harvested, and osteoclasts were quantified histomorphometrically. The results showed that neither treatment altered pressure-induced resorption. However, BW755c significantly increased resorption in unpressurized bone when compared with control values. Because BW775c blocks both lipoxygenase and cyclo-oxygenase pathways, the results suggest an alternate pathway in middle ear bone resorption.

Differential stimulation of prostaglandin G/H synthase-2 in osteocytes and other osteogenic cells by pulsating fluid flow

Mechanical stress produces flow of fluid in the osteocytic lacunar-canalicular network, which is likely the physiological signal for the adaptive response of bone. We compared the induction of prostaglandin G/H synthase-2 (PGHS-2) by pulsating fluid flow (PFF) and serum in osteocytes, osteoblasts, and periosteal fibroblasts, isolated from 18-day-old fetal chicken calvariae. A serum-deprived mixed population of primarily osteocytes and osteoblasts responded to serum with a two- to threefold induction of PGHS-2 mRNA. Serum stimulated PGHS-2-derived PGE(2) release from osteoblasts and osteocytes but not from periosteal fibroblasts as NS-398, a PGHS-2 blocker, inhibited PGE(2) release from osteocytes and osteoblasts with 65%, but not that from periosteal fibroblasts. On the other hand PFF (0.7 Pa, 5 Hz) stimulated (3 fold) PGHS-2 mRNA only in OCY. The related PGE(2) response could be completely inhibited by NS-398. We conclude that osteocytes have a higher intrinsic sensitivity for loading-derived fluid flow than osteoblasts or periosteal fibroblasts.

Mechanical stress induces COX-2 mRNA expression in bone cells from elderly women

Mechanical loading-induced fluid flow in the lacuno-canalicular network is a possible signal for bone cell adaptive responses. In an earlier study we found that pulsating fluid flow (PFF, 0.7+/-0.02 Pa, 5 Hz, 0.4 Pa/s) stimulates the production of prostaglandins by neonatal mouse calvarial cells. In addition, mRNA expression of the inducible form of cyclooxygenase (COX-2), but not the constitutive form (COX-1), the major enzymes in prostaglandin production, was increased by PFF. The present study was performed to determine whether human primary bone cells from the iliac crest, respond to mechanical stress in a similar way as neonatal mouse calvarial cells. We subjected bone cells originating from the iliac crest of nine elderly women, between 56 and 80 yr of age, for 1 h to PFF and measured prostaglandin production and COX-1 and COX-2 mRNA expression. One hour PFF treatment stimulated the release of PGE2 by 3.5 fold and PGI2 by 2.2 fold. PFF also increased the expression of COX-2 mRNA by 2.9 fold, but did not change COX-1 mRNA. No correlation was found between donor age and PFF effect, neither on prostaglandin production nor on COX-2 mRNA expression. This study shows that bone cells from the iliac crest of elderly women react to PFF treatment in a similar way as neonatal mouse calvarial cells, namely with increased production of prostaglandins and upregulation of COX-2 mRNA expression. These results suggest that human bone cells from the iliac crest and neonatal mouse calvarial cells share a similar mechanotransduction pathway.

Effect of pharmacological sympathectomy on osteoclastic activity in the gerbilline auditory bulla in vivo

Bone destruction causes hearing loss in various middle ear disorders. The mechanisms of such pathological remodeling are unknown. Unilateral surgical sympathectomy is known to induce resorption within mandibular and auditory bulla bone. Explanation of the cause of this effect, however, may be confounded by hemodynamic changes induced by hemicranial sympathectomy and by uncertainty as to the neuroanatomical origins of sympathetic fibers. In this study, gerbils were infused with guanethidine sulfate (GS) to evaluate the in vivo effects of systemic sympatholysis on auditory bone remodeling. In addition, to discount any direct osteolytic effect, GS was assessed of its bone resorbing activity in vitro by means of the calvarial calcium release assay. The in vitro study revealed GS to have no effect on calcium release. The in vivo study revealed GS to increase both the osteoclast surface and number. Guanethidine-induced sympathectomy has thus been shown to increase remodeling in gerbilline auditory bone, while no direct osteolytic effect could be measured in vitro.

Interleukin-1 alpha induced cyclooxygenase-2 expression in bone-derived endothelial cells

Histological studies have suggested that vascular endothelial cells in bone are members of a complex network that regulates bone development and remodeling by producing soluble factors or by mediating cell-cell adhesion. To clarify the role of bone-derived endothelial cell lines (BDECs) in bone remodeling, we established several clones of BDECs from the femurs of BALB/c mice after transformation with the SV40 virus. Then we examined the response of these clones to interleukin-1alpha (IL-1alpha). IL-1alpha is known to induce bone resorption in part by increasing the expression of cyclooxygenase-2 (COX-2) that is associated with the production of PGE2 in osteoblast-lineage cells. Treating the primary and established BDECs with IL-1alpha induced COX-2 mRNA expression. A transcriptional activation assay revealed that the treatment with IL-1alpha increased COX-2 promoter activity in a dose-dependent manner, and IL-1alpha promoted COX-2 protein expression in BDECs. Treatment with IL-1alpha promoted PGE2 production from BDECs in a dose-dependent manner. These results indicate that IL-1alpha stimulates PGE2 synthesis largely by inducing BDECs to express COX-2. Because PGE2 stimulates bone resorption, these vascular endothelial cells, as well as osteoblast cells, play important roles in bone remodeling.

Induction of cyclooxygenase-2 in human synovial cells by beta 2-microglobulin

BACKGROUND

Prostaglandins (PGs) are important mediators of inflammation in arthritis. We evaluated the role of the cycloxygenase-2 (COX-2) enzyme, which regulates PG biosynthesis, in osteoarthropathy associated with hemodialysis-associated amyloidosis (HAA) by characterizing COX-2 expression in beta 2-microglobulin-treated human synovial cells.

METHODS

We examined the effects of beta 2-microglobulin (beta 2m), a major constituent protein of amyloid fibrils in HAA, on the COX-2 protein and mRNA expression in human synovial cells using Western blot and reverse transcriptase-polymerase chain reaction.

RESULTS

beta 2m selectively increased the biosynthesis of COX-2 protein and induction of COX-2 mRNA in a dose-dependent manner. Immunoabsorption of beta 2m-containing media by anti-beta 2m-specific antibody abrogated beta 2m-mediated COX-2 expression on synovial cells. On the other hand, dexamethasone markedly suppressed the induction of COX-2 protein and mRNA in beta 2m-stimulated synovial cells.

CONCLUSIONS

Our results suggest that induction of COX-2 expression by beta 2m may be an important component of the inflammatory process in hemodialysis-associated osteoarthropathy.

Basic fibroblast growth factor induces cyclooxygenase-2 expression in endothelial cells derived from bone

Although histological studies have suggested that endothelial cells in bone (BDECs) are associated with some osteolytic bone diseases, it is still unclear how BDECs contribute to bone remodeling. Here we examined the response of BDECs to basic fibroblast growth factor (bFGF, FGF-2) using primary and cloned murine BDECs isolated from the femurs of BALB/c mice. Treatment of primary and cloned BDECs with bFGF induced cyclooxygenase-2 (COX-2) mRNA and protein expression. Furthermore, bFGF promotes the production of prostaglandin E2 (PGE2), which is known to be a potent stimulator of bone resorption and to induce osteoclast formation. Because the secretion of PGE2 was suppressed by COX-2 specific inhibitor NS-398 and by COX-2 antisense oligodeoxynucleotides, bFGF promotes the synthesis of PGE2 in a COX-2-dependent manner. Therefore, endothelial cells in bone are associated with bone remodeling by controlling COX-2 expression and consequently PGE2 production.

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 alpha subunit and the signal-transducing beta 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.

Periodontal pathogen-related stimulation indicates unique phenotype of primary cultured human fibroblasts from gingiva and periodontal ligament: implications for oral health disease

STATEMENT OF PROBLEM

The fibroblast is considered an important cellular component in periodontitis because it is the predominant cell type in periodontal connective tissue.

PURPOSE

The purpose of this study was to test whether gingival fibroblasts (GF) and periodontal ligament fibroblasts (PDLF) are heterogeneous in their production of inflammatory mediators associated with bone resorption in response to lipopolysaccharides from the gram-negative bacterium Porphyromonas gingivalis. To test this hypothesis, we (1) compared interleukin-6 production by cultured human PDLF and GF isolated from the same individual when exposed to P. gingivalis lipopolysaccharide; and (2) compared prostaglandin-E2 production by cultured human PDLF and GF isolated from the same individual when exposed to P. gingivalis lipopolysaccharide.

MATERIAL AND METHODS

Human periodontal ligament and gingival fibroblasts were cultured from biopsies and exposed to P. gingivalis lipopolysaccharide. Levels of interleukin-6 and prostaglandin-E2 secreted into culture supernatant were measured by enzyme-linked immunosorbent assay and the data analyzed. Gingival fibroblasts secreted similar interleukin-6 and elevated prostaglandin-E2 levels compared with unstimulated cells. Periodontal ligament fibroblasts secreted elevated levels of both mediators compared with unstimulated cells. Secreted levels of interleukin-6 and prostaglandin-E2 by primary gingival and periodontal ligament fibroblast cultures appear to differ when stimulated with a periodontal pathogen-related virulence factor.

CONCLUSION

The fibroblast of the periodontal ligament and the fibroblast of the gingiva may represent different phenotypes that play unique roles in tissue responses to implants.

The effects of acid glycosaminoglycans on neonatal calvarian cultures--a role of keratan sulfate in Morquio syndrome?

Morquio syndrome (mucopolysaccharidosis IV) presents with multiple bone dysplasia and is characterized by the inability to degrade keratan sulfate due to deficient N-acetylgalactosamine-6-sulfate sulfatase in Morquio A syndrome and deficient beta-D-galactosidase in Morquio B syndrome. The aim of our study was to investigate into the pathogenetic mechanism as it is not clear whether the accumulation of keratan sulfate is toxic for osteoblasts or inhibits osteoblast activity as e.g. bone resorption. The glycosaminoglycans keratan sulfate, heparan sulfate, dermatan sulfate, chondroitin-4,6-sulfate and hyaluronic acid were tested in rat neonatal calvarian cultures for their effects on bone resorption, osteoblast activity and toxicity. Bone resorption was evaluated by calcium release into the medium, osteoblast activity by the determination of alkaline phosphatase and toxicity by measuring lactate dehydrogenase in the culture media. Keratan sulfate had no effect on bone resorption but inhibited osteoblast activity at the low, nontoxic concentration of 10 ng per ml organ culture supernatant significantly (p<0.05). At a concentration of 100 ng per ml keratan sulfate revealed toxic effects as reflected by significantly (p<0.05) elevated lactate dehydrogenase activity. None of the other glycosaminoglycans inhibited osteoblast activities. Heparan sulfate showed at toxic levels (10 microg per ml supernatant) significantly increased bone resorption (p<0.05) accompanied by increased alkaline phosphatase activity. The specific keratan sulfate effects of inhibiting osteoblast activity and toxicity towards bone, which were never tested before, suggest a role for this glycosaminoglycan in the pathogenesis of bone dysplasia in Morquio syndrome.

Prostaglandin mediated modulation of transforming growth factor-beta metabolism in primary mouse osteoblastic cells in vitro

Prostaglandins and transforming growth factor-beta (TGF-beta) are both important local regulators of bone metabolism, but their actions on bone are complex. Prostaglandins mediate bone loss due to immobilization, but prostaglandin E2 (PGE2) treatment stimulates bone formation in vivo. TGF-beta may have both anabolic and catabolic effects on bone in vitro. In this study, we tested the effects of PGE2 on TGF-beta release and on TGF-beta messenger RNA (mRNA) levels in neonatal mouse calvarial cell cultures. We also examined the relationship between endogenous prostaglandin production as a result of mechanical stress and the release of TGF-beta. Addition of PGE2 (10(-8)-10(-6)M) to the culture medium stimulated the release of TGF-beta peptide (active plus latent) after 24 and 48 h in a dose-related manner. This upregulation was paralleled by an increased expression of TGF-beta mRNA levels. Mechanical stimulation by 1 h treatment with pulsating fluid flow (producing a shear stress of 0.5 +/- 0.02 Pa at 5 Hz) resulted 1 h posttreatment in increased production of PGE2, prostaglandin l2 (PGI2), and prostaglandin F2a. In addition, the release of TGF-beta activity but not TGF-beta peptide was decreased 24 h after PFF treatment. Addition of indomethacin, which blocks endogenous prostaglandin production, neutralized the effect of PFF treatment on TGF-beta activity, indicating that the effect of stress was mediated by endogenous prostaglandins. These results suggest that PGE2 and other prostaglandins (probably PGI2 and/or PGF2a) have opposite effects on TGF-beta metabolism in bone cells, as PGE2 upregulates TGF-beta expression and synthesis while other prostaglandins downregulate TGF-beta activation.

The effects of exogenous prostaglandin E2 on root resorption in rats

This study evaluated the amount and depth of root resorption associated with varying concentrations and frequencies of injectable, exogenous prostaglandin E2 (PGE2) in conjunction with orthodontic tooth movement in rats. The sample consisted of 155 maxillary right and left first molars from 88, 8-week old, male Sprague-Dawley rats. The animals were divided into three control groups and two experimental groups. The control animals were divided into one nonappliance and two appliance groups. The experimental animals were divided into 2- and 4-week experimental time periods that were further subdivided based on single and weekly injection intervals of PGE2 and four different injectable concentration levels, i.e., 0.1, 1.0, 5.0, and 10.0 micrograms. A fixed orthodontic appliance was ligated between the maxillary incisors and maxillary first molars with closed-coil nickel-titanium springs. The appliance had an initial activating force of 60 gm. Serial histologic sections of the mesial root of the maxillary first molar were made, and a quantitative histomorphometric analysis of root resorption on the mesial and distal surfaces was performed. This study demonstrated increased root surface resorption when using exogenous PGE2 injections to enhance orthodontic tooth movement over a 2-week period with increasing root resorption on the mesial surface as compared with the distal surface in PGE2 treated teeth. No differences in root resorption were found with either multiple injections or increasing concentration in the 4-week experimental group. Local injection of PGE2 appeared to have no effect on the number or depth of resorption lacunae in either the 2- or 4-week groups.

Prostaglandin E2 induces Egr-1 mRNA in MC3T3-E1 osteoblastic cells by a protein kinase C-dependent pathway

Prostaglandin E2 (PGE2) plays an important role in the regulation of osteoblast metabolism. However, the nuclear signal transduction mechanisms involved in the actions of PGE2 have not been clearly defined. One mechanism may involve induction of immediate early genes such as the transcription factor Egr-1. In the present study, we examined the effects of PGE2 on induction of Egr-1 mRNA in MC3T3-E1 osteoblasts. Time course studies with 2 microM PGE2 showed maximal induction of Egr-1 mRNA at 30 min. In cells pretreated with cycloheximide (CHX), induction of Egr-1 mRNA reached a maximum at 60 min and remained elevated for at least 240 min. Preincubation with CHX was associated with superinduction of Egr-1. Inhibition of protein kinase C activity by pretreatment with 1 microM chelerythrine chloride or by prolonged stimulation with 50 ng/ml tetradecanoyl phorbol acetate (TPA) attenuated the induction of Egr-1 mRNA by 2 microM PGE2. These data indicate that in MC3T3-E1 cells, PGE2 increase Egr-1 mRNA levels via a protein kinase C-dependent pathway.

Effect of eicosapentaenoic acid and docosahexaenoic acid on diabetic osteopenia

To evaluate the effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are polyunsaturated fatty acids, on diabetic osteopenia, we measured the bone fragility in streptozotocin-induced diabetic rats. The fragility of femur was increased in diabetic rats, which was prevented in part by EPA or DHA. Moreover, EPA prevented osteopenia even in diabetic rats fed a low zinc feed, which was a potent accelerator of diabetic osteopenia. Plasma alkaline phosphatase activity and parathyroid hormone level showed no difference between the two groups of diabetic rats with or without EPA. Urinary excretion of calcium and phosphate was increased and plasma inorganic phosphate level was high in diabetic rats, suggesting severe mineral loss. In diabetic rats fed EPA, although urinary and plasma calcium levels did not change significantly, urinary phosphate excretion and plasma inorganic phosphate concentration were slightly lowered, which suggested that EPA may have an effect in suppressing phosphate release from bones in diabetic rats. These data suggest that EPA and DHA could be effective on diabetic osteopenia, but to elucidate the precise mechanisms, further examinations will be needed.

The effects of exogenous prostaglandins on orthodontic tooth movement in rats

The long-term effects of varying concentrations and frequencies of injectable, exogenous prostaglandin E2 (PGE2) on the rate of tooth movement and the amount of root resorption were evaluated. There were 132 male Sprague-Dawley rats 8 weeks old that initially weighed 225 to 250 gm. Five animals were in a pilot study, while seven were baseline controls and eight were appliance controls. The remaining 112 animals were divided into two experimental time periods of 2 and 4 weeks. Then, each experimental time period was divided into four subgroups of 14 animals based on concentration levels of PGE2 injections, i.e., 0.1, 1.0, 5.0 and 10.0 micrograms. Half of these animals in the dosage subgroup received a single injection at appliance placement and the other half received weekly injections. A fixed orthodontic appliance consisting of closed-coil nickel-titanium springs were ligated between the maxillary incisors and maxillary first molars. The initial activating force was 60 gm. The results showed that injections of exogenous PGE2 over an extended period of time in rats did enhance the amount of orthodontic tooth movement. However, there was no statistically significant difference in tooth movement between the single and multiple injection groups or among the four concentration levels of PGE2 used in either the 2- or 4-week time periods. The amount of root resorption as seen from scanning electron micrographs did increase with the use of prostaglandin injections, specifically with increased numbers of injections and with increased concentrations of PGE2.

Age-dependent stimulation or inhibition of calcium release from bone cultures by interleukin-1 beta

Previous studies have shown that interleukin-1 beta (IL-1 beta) is a potent bone resorption stimulating agent in cultures of fetal or neonatal bones. In the present study, evidence has been provided showing that this cytokine failed to stimulate bone resorption in cultured 75-day-old mouse calvaria maintained in a chemically defined medium for 14 days, as determined by measuring calcium release into the medium and histological examination of cultured bones. Moreover, the cytokine significantly inhibited basal bone resorption in cultured 75-day-old mouse calvaria, a finding reminiscent of the paradoxical effect observed with 1 alpha,25-dihydroxycholecalciferol. Since IL-1 beta did not alter the number of osteoclasts present in the cultured older calvaria as compared to the untreated control, we hypothesized that in such cultured older bones the cytokine affects primarily the function rather than proliferation/differentiation of osteoclasts, either directly or indirectly through its action on other cells in bone tissue, such as osteoblasts or stromal cells. Also, it is possible that the cytokine affects the formation and/or function of macrophages that have been shown to participate in the bone resorption process. These findings support the concept that at different stages of host maturation, bone tissue may exhibit a different response to the same osteotropic agent.

Role of IL-1 beta and prostaglandins in beta 2-microglobulin-induced bone mineral dissolution

beta 2-microglobulin (beta 2m) induces an osteoclast-mediated net calcium efflux from neonatal mouse calvariae which occurs only after 48 hours of incubation, suggesting that beta 2m acts via other growth factors. To further test this hypothesis, calvariae were incubated with and without beta 2m in the presence of the prostaglandin inhibitor indomethacin, anti-interleukin-1 beta antibody (anti-IL-1 beta), or interleukin-1 beta receptor antagonist (IL-1 beta RA). The addition of beta 2m to the culture medium stimulated, whereas indomethacin inhibited basal calcium efflux following 48 hours. However, the difference (delta) between the calcium efflux induced in calvariae incubated with and without beta 2m in basal medium and that in calvariae incubated with and without beta 2m in indomethacin supplemented medium was similar, suggesting a prostaglandin independent mechanism. There was a time dependent increase in PGE2 in basal medium which was unaffected by beta 2m. In contrast, pre-incubating calvariae with either anti-IL-1 beta or IL-1 beta RA did not alter basal calcium efflux but completely blocked the beta 2m induced calcium efflux. Anti-IL-1 beta had no effect on the basal release of beta-glucuronidase but partially blocked the beta 2m induced release of beta-glucuronidase. Thus, the beta 2m-induced calcium efflux observed in neonatal mouse calvariae is dependent on interleukin-1 beta but not prostaglandins.

Effect of different magnitudes of tension force on prostaglandin E2 production by human periodontal ligament cells

Periodontal ligament (PDL) cells are known to produce prostaglandin E2 (PGE2) in response to mechanical stress. However, the rate of PGE2 production from PDL cells in response to different magnitudes of tension forces has not been examined. This study, therefore, was undertaken to determine the effect of different magnitudes of tension forces on PGE2 production and inositol trisphosphate (IP3) levels in PDL cells in vitro. Human PDL cells were cultured on flexible-bottomed plates and placed on a Flexercell strain unit. Cells were flexed at six cycles (5-s strain, 5-s relaxation) at six steps of tension force (9, 12, 15, 18, 21, 24% increase in surface area) for 5 days. PGE2 production and IP3 levels were determined by radioimmunoassay. There was a 6- and 25-fold increase in the rate of PGE2 production by cells exposed to low (9%) and high (24%) tension forces, respectively, and these increases were tension force-dependent. Tension force also induced increases in the intracellular levels of IP3 that did not seem to be directly related to the production of PGE2. The different rates of PGE2 production by PDL cells in response to different magnitudes of mechanical stress may be of importance in PDL and alveolar bone metabolism.

Indomethacin has distinct early and late actions on bone formation induced by mechanical stimulation

The capacity of bone to adapt its architecture in response to changing mechanical demands is well recognized. However, the mechanisms by which mechanical stimuli are translated into new bone formation are poorly understood. Prostaglandins (PGs) may play a role. We therefore tested the effect of indomethacin on the cancellous bone formation induced by mechanical stimulation in the 8th caudal vertebrae of adult rats. Rats were given indomethacin 3 h before loading, 3 h before loading and daily thereafter, 6 h after loading, or 6 h after loading and daily thereafter. The increase in bone formation caused by loading was suppressed by a single dose of indomethacin if given before but not after loading. Daily administration of indomethacin suppressed the mechanical response, even when started after loading. These results suggest that PGs are essential for the transduction of mechanical stimuli into bone formation, and also that there may be two distinct phases of PG dependency in the response of bone to mechanical loading: an early phase associated with the immediate loading period and a later phase associated with osteogenic interactions entrained by the early phase.

Prostaglandin E2 activity in the synovial-like membrane

The events leading to aseptic loosening of total hip prostheses occur within the synovial-like membrane that forms around the prosthetic components. Prostaglandin E2 (PGE2) activity in this membrane is believed to be one of the factors that cause aseptic loosening. In this study, the authors investigated the correlation between grades of loosening and levels of PGE2-like activity in the membranes surrounding the implants in 14 patients in which total hip arthroplasty revisions were performed. The membranes of patients with high degrees of loosening demonstrated high levels of PGE2-like activity (P < .01). Among the many factors contributing to loosening of total hip arthroplasties, PGE2 appears to have an important role with its bone-resorbing properties.

Eicosapentaenoic acid inhibits bone loss due to ovariectomy in rats

Eicosapentaenoic acid (EPA), one of the polyunsaturated fatty acids, is well-known to have a wide variety of beneficial biological functions. In the present work we demonstrate another new beneficial effect of EPA on bone metabolism in vivo. Ovariectomized rats were divided into 4 groups under the same calorie intake condition; (1) normal diet, (2) low calcium diet (1.5 mg/day), (3) EPA-enriched diet (160 mg/day/kg), (4) EPA-enriched and low calcium diet. These diets were continued for 35 consecutive days. The bone weight of the femora and tibiae decreased significantly in the low calcium group, but the decrease was inhibited in the EPA-low calcium group. Moreover, in the rupture test, which indicates bone strength, the femora in the low calcium group were easier to break than in the normal calcium diet groups. In the EPA-low calcium group the strength of the bone was equivalent to that in the normal diet group. These results suggest that an EPA-enriched diet prevents the loss of bone weight and strength caused by oestrogen deficiency or inadequate nutrition. There is a possibility that EPA could be developed to be a novel anti-osteoporosis drug.

Dietary lipids, prostaglandin E2 levels, and tooth movement in alveolar bone of rats

A previous study showed that certain dietary lipids can alter arachidonic acid concentrations in alveolar bone. Because arachidonic acid is a precursor of prostaglandin (PG) E2, which is known to play an important role in orthodontic tooth movement, the purpose of the present study was to determine the effect of dietary lipids on PGE2 levels and tooth movement. Two groups of male Sprague-Dawley rats (20/group) were fed nutritionally adequate purified diets containing 10% corn oil (group I, rich in n-6 fatty acids) or 9% ethyl ester concentrate of n-3 fatty acids + 1% corn oil (group II rich in n-3 fatty acids). After 5 weeks of feeding the diets, orthodontic force of 56 g was applied to the maxillary incisors to tip them distally. Prior to killing the rats at day 4 and 8 of orthodontic force application, tooth movement was measured by computerized image analysis. Premaxillae were dissected out free of soft tissue and incisors. The alveolar bone was frozen in liquid nitrogen, pulverized, and lipids were extracted. The concentrations of arachidonic acid and fatty acid composition of total phospholipids were measured by gas chromatography. PGE2 levels were measured by enzyme immunoassay. Arachidonic acid and PGE2 concentration were significantly lower (P < 0.001) in alveolar bone of rats in group II than in group I. The tooth movement was also significantly lower (P < 0.02) in group II than in group I at both 4 and 8 days. The results suggest that PGE2 levels in alveolar bone and orthodontic tooth movement can be affected by the type of dietary fat.

Effects of hormones and cytokines on stimulation of adenylate cyclase and intracellular calcium concentration in human and canine periodontal-ligament fibroblasts

Adenylate cyclase was stimulated by prostaglandin E2 (PGE2) and parathyroid hormone-related protein (PTHrP) in both these types of fibroblast and by calcitonin gene-related protein (CGRP) in the human fibroblasts in vitro. PGE2 (1 microM), CGRP (1 microM), and PTHrP (1 microM) stimulated adenylate cyclase up to 50-fold, 10-fold and 9-fold, respectively. Calcitonin (CT), substance P (SP), interleukin-1 beta (IL-1 beta), and transforming growth factor-beta 1 (TGF beta 1) had no effect on adenylate cyclase in either fibroblast. Intracellular Ca2+ (iCa2+) was measured in individual fibroblasts from the periodontal ligament using Indo-1 and an adherent cell analysis and sorting interactive laser cytometer. Ionomycin (3 microM) caused a transient rise of iCa2+ in all human and canine fibroblasts tested. The mean percentage increase in iCa2+ in response to ionomycin was 820 and 840% for human and canine fibroblasts, respectively. The human fibroblasts responded to PGE2 (1 microM) by an increased iCa2+ concentration; the mean percentage increase in iCa2+ was 187%. SP caused a less pronounced increase in iCa2+ in the human fibroblasts (56%). CGRP and SP caused a similar response in the canine fibroblasts. The mean percentage increase in iCa2+ in response to SP and CGRP was 95 and 78%, respectively. PTH, PTHrP, platelet-activating factor, CT, and IL-1 beta had no effect on iCa2+ in either type of fibroblast. The data indicate that cAMP and calcium have roles as intracellular secondary messengers in the action of PGE2, SP, CGRP, and PTHrP in fibroblasts of human and canine periodontal ligament.

Effects of interleukin-1 alpha on arachidonic acid metabolism in human osteosarcoma osteoblastic cells

The effects of interleukin-1 alpha (IL-1 alpha) on arachidonic acid (AA) metabolism were studied in the human osteosarcoma cell lines, G292 and SaOS-2. The cells were prelabeled with 3H-arachidonic acid. Radiolabeled metabolites were measured by reversed-phase high-pressure liquid chromatography with a radioactive detector. Indomethacin inhibited prostaglandin E2 (PGE2) production without affecting lipoxygenase (LO) products in G292 cells. In the G292 cells, IL-1 alpha (50 U/ml) induced a 10-fold increase in PGE2 production at all the incubation times tested, and a significant two-fold increase in 5 hydroxyeicosatetraenoic acid (HETE) formation after 48 h. These effects were not seen in SaOS-2 cells under identical conditions. These results suggest that, although some osteosarcomal cell lines may not respond directly to IL-1 with effects on AA metabolism, the mechanism of its action in others may involve modulation of both cyclooxygenase (CO) and LO pathways.

Systematic assessment of bone resorption, collagen synthesis, and calcification in chick embryonic calvaria in vitro: effects of prostaglandin E2

A systematic method has been developed to assess bone resorption, matrix formation, and calcification in a single calvarial culture from 20-day-old chick embryos. The bones were prelabeled with 45Ca by an injection into the egg white before culture. In the last 2 h of incubation, the bones were further labeled with both 3H-proline and 3H-tetracycline. Bone resorption was assessed as 45Ca release into the medium. Collagen synthesis was measured by the incorporation of 3H-proline into collagenase-digestible protein (CDP). Since tetracycline has been commonly used as an in vivo marker for osteoid calcification, we assessed in vitro calcification as the uptake of 3H-tetracycline into bone. By using this method, we studied the effects of prostaglandin E2 (PGE2) and indomethacin, which inhibits biosynthesis of PGE2, on bone resorption and formation. The cultured bone synthesized approximately 300 ng of PGE2 during every 24 h of incubation, and indomethacin (10(-6) M) completely inhibited the synthesis. In indomethacin-treated cultures, % 45Ca release and the labeling of CDP were significantly reduced. These reductions were not seen when exogenous PGE2 (10(-9) M) comparable to its endogenous level was added along with the indomethacin. Furthermore, 10(-8) to 10(-5) M PGE2 increased % 45Ca release and the CDP labeling. In addition, the uptake of 3H-tetracycline into the cultured bone was also enhanced by PGE2. In devitalized calvaria, PGE2 had no effect on 3H-tetracycline uptake, suggesting that the stimulative effect on PGE2 was cell-mediated.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins: mechanisms of action and regulation of production in bone

Prostaglandins (PGs), particularly PGE2, are produced by bone and have powerful effects on bone metabolism. PGs have an initial, transient, direct inhibitory effect on osteoclast function. However, the major long-term effect in bone organ culture is to stimulate bone resorption by increasing the replication and differentiation of new osteoclasts. PGs also stimulate osteoclast formation in cell culture systems. Stimulation of osteoclastic bone resorption may be important in mediating bone loss in response to mechanical forces and inflammation. PGs have a biphasic effect on bone formation. At relatively low concentrations or in the presence of glucocorticoids, the replication and differentiation of osteoblasts is stimulated and bone formation is increased. This increase is associated with an increase in production of insulin-like growth factor-I (IGF-I). However, at high concentrations or in the presence of IGF-I, PGE2 inhibits collagen synthesis. In osteoblastic cell lines this inhibition can be shown to occur at the level of transcription of the collagen gene. The stimulatory effect on bone formation has been demonstrated when PGs are administered exogenously, but it is not clear how endogenous PG production affects bone formation in physiological or pathologic circumstances. The production of PGs in bone is highly regulated. The major source appears to be cells of the osteoblast lineage. A major site of regulation is at the level of the enzyme PG endoperoxide synthase (cyclooxygenase or PGH synthase). PGE2 production and PGH synthase mRNA are increased by PTH and interleukin-1 and decreased by estrogen. Glucocorticoids probably act by a different mechanism, decreasing either arachidonic acid or PGH synthase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonsteroidal antiinflammatory drugs as inhibitors of periodontal disease progression

Recent interest in the control and modulation of periodontal disease has focused on the potential benefits of blocking the host response mechanisms involved in the progression of the disease. In addition to recent advances in the identification and control of etiologic bacteria, investigators have indicated promising results using nonsteroidal antiinflammatory drugs (NSAIDs) as inhibitors of the inflammatory destruction in periodontal disease. This article examines research efforts over the last 20 years describing the role of prostaglandins in periodontal disease and the effect of NSAIDs on the progression of gingival inflammation and alveolar bone loss.

Regulation of ornithine decarboxylase by parathyroid hormone in osteoblastic cell systems

Parathyroid hormone (PTH) has been shown to induce osteoblastic activity via a complex signal transduction process which is mediated either by cAMP or cytosolic calcium ([Ca2+]i), or a combination thereof. One of the PTH functions in osteoblasts is the induction of ornithine decarboxylase (ODC) activity. We have analyzed the second messengers involved in this process. 8-Bromo cAMP, a cAMP derivative, enhanced ODC activity in UMR106-01 osteoblastic cell system. The calcium ionophore A23187 and the protein kinase stimulator phorbol-12-myristate 13-acetate did not alter ODC activity. ODC activity was increased by bPTH-(1-34), PGE1, and PGE2 which stimulated both cAMP and [Ca2+]i. In contrast, PTH-(2-34), propionyl bPTH-(2-34), bPTH-(3-34), bPTH-(7-34), and PGF2 alpha, which only enhanced [Ca2+]i but not cAMP, had no effect on ODC activity. Thus, the stimulation of ODC in UMR106 cells by PTH appeared to be mediated primarily via the cAMP signal transduction pathway, and the mere increase in intracellular calcium could not account for the stimulation of ODC activity. ODC mRNA level was found to be increased by PTH treatment. Therefore, translation of ODC may be stimulated by PTH. Moreover, PTH also stimulated ODC antizyme activity, suggesting that the ODC degradation rate was increased.

A simple method to assess osteoclast-mediated bone resorption using unfractionated bone cells

To determine osteoclastic bone resorption we established a simple assay system in which unfractionated cells obtained from femora of 13-day-old mice were cultured on a dentine slice and the number of osteoclasts and their induced pit area on the slices were measured. When the bone cells (1 x 10(5) cells/dentine slice) were cultured in the presence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] or human parathyroid hormone (hPTH) for 4 days, at which time newly-formed osteoclasts were not detected, the pit area was dose-dependently increased, being a 4.3- or 4.1-fold respective increase over the control at a 10(-8) M concentration of hormones. Chick calcitonin (cCT) inhibited the osteoclastic bone resorption induced by either of these hormones. cCT alone also suppressed the bone resorption by the cells (3 x 10(5) cells/dentine slice). These findings indicate that 1,25(OH)2D3 or hPTH may mainly activate pre-existing osteoclasts, resulting in increased bone resorption, and that cCT may suppress this osteoclastic activity. When 1,25(OH)2D3 or hPTH was added to the cells pre-cultured in factor-free medium for 6 days, at which time pre-existing osteoclasts had almost degenerated, new osteoclasts were formed, resulting in an increase in pit formation. Thus this system is a useful method which could more sensitively evaluate the effects of hormones or factors on osteoclast formation and activation than other previous systems.