Estrogenic pyrethroid pesticides regulate expression of estrogen receptor transcripts in mouse Sertoli cells differently from 17beta-estradiol.

Studies suggested that exposure to agricultural pesticides may affect male fertility. Pyrethroids are widely used pesticides due to their insecticidal potency and low mammalian toxicity. A recombinant yeast assay system incorporating the human alpha-estrogen receptor was used to analyze the estrogenicity of a range of readily available pyrethroid pesticides. The commercial product Ripcord Plus showed estrogenic activity by this assay. To determine whether pyrethroid compounds might exert an effect on male fertility, mouse Sertoli cells were exposed in vitro to the endogenous estrogen, 17beta-estradiol, and selected estrogenic pyrethroids. Following exposure, transcript levels of the alpha- and beta-estrogen receptors were assessed. Exposure of Sertoli cells to the pyrethroid compounds, both at high and at low published serum concentrations, affected the expression of the two estrogen receptors; however, the influence on estrogen receptor gene expression was different from the effect from exposure to 17beta-estradiol. These results from our model systems suggest that (1) estrogenic pyrethroid pesticides affect the estrogen receptors, and therefore potentially the endocrine system, in a different manner from that of endogenous estrogen, and (2) should cells in the male testes be exposed to pyrethroid pesticides, male fertility may be affected through molecular mechanisms involving estrogen receptors.

Stability of added iodine in processed cereal foods.

The stability of iodine from iodized salt was measured in white bread, grain bread, sweet biscuits and the breakfast cereals, Weetbix (a flaked, pressed, wheat product), Ricies (a puffed rice product) and toasted muesli, as part of the New Zealand Government's initiatives to address the public health issue of low iodine intake by most New Zealanders. Triplicate runs of each product were manufactured by commercial food manufacturers between September 2006 and May 2007 with iodized and non-iodized salt. Triplicate samples were taken at various steps during processing of each food and analysed for moisture and iodine content. Iodine concentration was determined by inductively coupled plasma-mass spectrometry following an alkaline digestion. Iodine, at the equivalent of 25-65 mg of iodine per kg salt, was 100% retained in each of the selected foods from the time of mixing to the final product. These results imply that all iodine added via salt at the time of manufacture is available for consumption but not necessarily bioavailable. These data can be used for modelling the impact of strategies to increase iodine exposure. Salt as an ingredient is not a good predictor of iodine intake due to the inhomogeneity of iodine in iodized salt.

Intake and risk assessment of nitrate and nitrite from New Zealand foods and drinking water.

Exposure to excess nitrite is a potential health risk for humans. One hundred meat and processed foods and 100 vegetable samples purchased from New Zealand retail outlets were prepared as for consumption and analysed for nitrite and nitrate concentration using a standard, validated methodology. Nitrate concentrations ranged from less than the limit of detection (LOD = 5 mg kg-1) in cheddar cheese and cream cheese-based dips to 3420 mg kg-1 in lettuce. Nitrite was detected in half the processed foods and meats analysed (levels up to 119 mg kg-1), but detected in only one vegetable sample above the LOD (broccoli at 27 mg kg-1 nitrite). Concentration data were combined with 24 h dietary recall information to generate 4398 individual adult daily exposure scenarios for exogenous nitrite and nitrate including a contribution from water assessed from 1021 drinking water samples. The mean adult daily intake of exogenous nitrate and nitrite from food and water combined was 16 and 13% of the Acceptable Daily Intake (ADI), respectively, and therefore should not pose a health risk for the average consumer. A maximally exposed New Zealand adult is estimated to have an intake of up to seven times the ADI for nitrate. When the endogenous conversion of nitrate to nitrite is taken into account, approximately 10% of people with an average rate of conversion and half of all people with a high rate of conversion are estimated to exceed the ADI. Either the ADI is inappropriate and needs to be re-evaluated, or those individuals who have a high rate of conversion of nitrate to nitrite are at risk to adverse effects of nitrite exposure.

Bisphenol A in canned foods in New Zealand: an exposure assessment.

Exposure to bisphenol A (BPA) from the consumption of canned and bottled food has been determined for New Zealand adults. Eighty different canned foods purchased from retail outlets in Christchurch, New Zealand, between November 2003 and February 2004 were analysed for BPA concentration by gas chromatography/mass spectrometry. BPA was detected in all foods analysed except for soft drinks. Concentrations ranged from < 10 to 29 microg kg(-1), except for individual samples of tuna, corned beef and coconut cream, which were 109, 98 and 191 microg kg(-1) , respectively. The limit of quantitation was <10 microg kg(-1) for foods of low fat content (< 1%) and <20 microg kg(-1) for foods containing >1% fat. Mean concentration data were combined with 24-h dietary recall information for 4399 individual consumers. Mean and maximum exposures were 0.008 and 0.29 microg kg(-1) bw day(-1), respectively, well below the temporary tolerable daily intake of 10 microg kg(-1) bw day(-1) given by the European Commission in 2002. The results of the present survey suggest that the levels of BPA identified in canned foods are unlikely to be of concern to adult health, and there is no reason for consumers to change their consumption patterns as a result of these findings. When the concentration data found in the current survey are applied to an oestrogenicity model for an adult male, the contribution of BPA to the total oestrogenicity from 16 food components is 7%. The impact of this level of oestrogenicity remains unclear.

The cellular responses of articular cartilage to sharp and blunt trauma.

OBJECTIVE: To determine the response of immature articular cartilage to both sharp and blunt trauma in terms of cell death, cell proliferation and matrix synthesis. DESIGN: Blunt wounds were made with a trephine in full depth immature bovine articular cartilage explants which were cut in half through the center of the trephine wound with a sharp scalpel to produce blunt and sharp trauma on the same explant. Explants were maintained in culture for up to 10 days. Prior to fixation at days 2, 5 and 10, medium was supplemented with 10 microCi ml-1 35S-sulphate, [3H]-proline or [3H]-thymidine for 24h to assess matrix synthesis and cell proliferation. Cell death was assessed using a Live/Dead label. RESULTS: In the case of blunt wounds, a band of cell death was observed adjacent to the lesion edge. Microautoradiography demonstrated little radiolabel incorporation and, therefore, no new matrix synthesis or cell proliferation within this region. In contrast, wounds made with a sharp scalpel showed restricted cell death, with radiolabel incorporation adjacent to the lesion edge at all time points. This demonstrated not only chondrocyte proliferation and new matrix synthesis at the wound margin, but also an up-regulation of matrix synthesis adjacent to the lesion edge. CONCLUSIONS: In terms of clinical relevance, the use of sharp precise instruments during the surgical management of cartilage defects may be necessary to reduce cell death and promote matrix elaboration at the lesion edge in order to facilitate successful integration.

Permanganate oxidation of sorbed polycyclic aromatic hydrocarbons.

The polycyclic aromatic hydrocarbons (PAH) that contaminate soils at many industrial and government sites are resistant to natural biotic and abiotic degradation processes. The recalcitrant nature of these compounds may require aggressive chemical treatment to effectively remediate these sites. This study was conducted to assess the viability of permanganate oxidative treatment as a method to reduce PAH concentration in contaminated soils. Study results demonstrated a reduction in soil sorbed concentration for a mixture of six PAHs that included anthracene, benzo(a)pyrene, chrysene, fluoranthene, phenanthrene, and pyrene by potassium permanganate (KMnO4) oxidative treatment. The greatest reduction in soil concentration was observed for benzo(a)pyrene, pyrene, phenanthrene, and anthracene at 72.1, 64.2, 56.2, and 53.8%, respectively, in 30 min at a KMnO4 concentration of 160 mM. Minimal reductions in fluoranthene and chrysene concentration were observed at 13.4 and 7.8%, respectively, under the same conditions. A relative chemical reactivity order of benzo(a)pyrene>pyrene>phenanthrene>anthracene>fluoranthene>chrysene towards permanganate ion was observed. Aromatic sextet theory was applied to the degradation results to explain the highly variable and compound-specific chemical reactivity order.

Expression of clusterin in the superficial zone of bovine articular cartilage.

OBJECTIVE: To investigate the differences between chondrocytes of the superficial and underlying zones of articular cartilage at the level of gene expression. METHODS: Messenger RNA (mRNA) was isolated from chondrocytes harvested from the superficial and deep zones of immature bovine articular cartilage. This mRNA was reverse transcribed, radiolabeled, and then each complementary DNA (cDNA) sample was used to screen duplicate filters of a bovine chondrocyte cDNA library. By comparing autoradiographic signals on matching filter sets, clones exclusively expressed in the superficial zone of articular cartilage were isolated and characterized further. RESULTS: Of the superficial-specific gene clones isolated, 25% were found to be a single gene product, clusterin. Northern hybridization was used to show that clusterin is expressed specifically in the superficial zone of articular cartilage and that its expression is up-regulated in mature cartilage. In situ hybridization was used to precisely localize clusterin transcripts in articular cartilage, where it was found that clusterin expression was confined to the articular surface in both immature and mature samples. CONCLUSION: The discovery of clusterin expression at the articular cartilage surface extends previous observations that superficial articular chondrocytes are highly specialized cells. Clusterin is a multifunctional, secreted glycoprotein that has been shown to be expressed in diverse locations that have in common a tissue-fluid boundary. Additionally, clusterin has been implicated in regulating complement activation and cell death in injured and degenerating tissues.

The reactions of articular cartilage to experimental wounding: role of apoptosis.

OBJECTIVE: To determine the cellular and matrix responses to experimental wounding of articular cartilage. METHODS: Immature and mature bovine articular cartilage was used as an in vitro model system to study the cellular responses to cartilage wounding. Explant cultures were wounded centrally with a trephine and maintained for up to 10 days. TUNEL labeling together with ultrastructural analyses were used to assess the nature of the observed cell death. In vitro labeling with 3H-thymidine was used to detect cell proliferation, and 2 antibodies (COL2-3/4M and BC-13) were used to detect changes in matrix turnover. RESULTS: Cell death was observed as a response to wounding and was considered to be a combination of necrosis and apoptosis. In immature tissue, cell death was more pronounced, particularly in the articular surface region. Within the area of cell death, many cells that did not die subsequently underwent proliferation. The collagenous network showed evidence of denaturation in the area of the wound, but "aggrecanase" activity was not detected. CONCLUSION: There are 2 contrasting, but related, responses to cartilage wounding--apoptosis and proliferation. In order to improve cartilage repair, future studies need to elucidate the regulatory mechanisms that determine these responses.

Reduction of Cr, Mo, Se and U by Desulfovibrio desulfuricans immobilized in polyacrylamide gels.

Intact cells of Desulfovibrio desulfuricans, immobilized in polyacrylamide gel, removed Cr, Mo, Se and U from solution by enzymatic-mediated reduction reactions. Lactate or H2 served as the electron donor and the oxidized Cr(VI), Mo(VI), Se(VI) and U(VI) served as electron acceptors. Reduction of the oxidized metal species resulted in the precipitation of solid phases of the metals. Metal removal efficiencies of 86-96% were achieved for initial concentrations of 1 mM Mo, Se, and U and 0.5 mM Cr. Insoluble metal phases accumulated on both the surface and the interior of the polyacrylamide gel. In column tests conducted for U removal, effluent concentrations less than 20 micrograms L(-1) were achieved with initial concentrations of 5 mg L(-1) and 20 mg L(-1) U and residence times from 25-37 h. The enzymatic reduction of Cr, Mo, Se, and U by immobilized cells of D. desulfuricans may be a practical method for removing these metals from solution in a biological reactor.

Removal of U and Mo from water by immobilized Desulfovibrio desulfuricans in column reactors.

Intact cells of Desulfovibrio desulfuricans were immobilized in polyacrylamide gel and used to remove soluble U and Mo from water by enzymatically mediated reduction reactions in column reactors. Formate or lactate served as the electron donor and oxidized U(VI) and Mo(VI) species served as electron acceptors. Greater than 99% removal efficiencies were achieved for both metals with initial concentrations of 5 mg/L U and 10 mg/L Mo. Hydraulic residence times in the columns were between 24 and 36 h. Sulfate concentrations as high as 2000 mg/L did not inhibit reduction of U or Mo in the columns. However, nitrate inhibited uranium reduction at concentrations near 50 mg/L and inhibited molybdenum reduction at concentrations near 150 mg/L. The results indicate that enzymatic reduction of U and Mo by immobilized cells of D. desulfuricans may be a practical method for removing these contaminants from solution in continuous-flow reactors.

Dextran sulfate promotes the rapid aggregation of porcine bone-marrow stromal cells.

Despite the fact that cells of the mammalian stromal compartment of bone marrow have been shown to contain multipotential stem cells when studied in diffusion chambers it is notable that the same range of possible phenotypes (e.g., chondrocytic) has not been induced in freshly isolated marrow stromal cells in vitro. To investigate the possible role of glycoconjugates on phenotype expression, the effects of chondroitin sulfate, dermatan sulfate, dextran 500, and dextran sulfate on the cell morphology and differentiation of confluent porcine bone-marrow stromal-cell monolayers were studied. Of these glycosaminoglycan molecules only dextran sulfate induced confluent porcine bone-marrow stromal-cell monolayers to retract into tight, circular cell aggregates. Retraction began within 6 h, was complete after 3-5 days, and was dose dependent. Subsequent removal of dextran sulfate from the culture medium resulted in a return to a monolayer culture. Aggregated cells were essentially nonmitotic but dye exclusion indicated high cell viability. Dexamethasone, ascorbate, and beta-glycerophosphate produced no morphological change within 6 days when administered alone, but increased proliferation and aggregation in dextran sulfate-treated cultures. Immunocytochemistry of monolayer cultures revealed positive staining for type I but not type II collagen and addition of dexamethasone, ascorbate, and beta-glycerophosphate increased type I collagen deposition. In contrast, the centers of dextran sulfate-induced aggregates were positive for type II collagen, whereas type I collagen was only present at the periphery of the aggregates. Further addition of dexamethasone, ascorbate, and beta-glycerophosphate had little effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a polyclonal antiserum to rat growth hormone on circulating insulin-like growth factor (IGF)-I and IGF-binding protein concentrations and the growth of muscle and bone.

A polyclonal antiserum to rat GH (anti-rGH) injected into rats for 3 or 8 weeks markedly reduced the weight, total protein and RNA content of muscles of the hind limb. These effects were prevented when bovine GH (bGH) was administered simultaneously. In a second experiment, the effects of 8 weeks of treatment with anti-rGH on the growth of the whole body, muscle and bone were investigated. Body weights of rats were decreased by 58% by treatment with anti-rGH; muscle weights were reduced by slightly more than the decrease in body weight (by 64%, 65% and 61% respectively for plantaris, soleus and gastrocnemius). The weight of the tibia was decreased by 54%, its length was decreased by 23%, cortical width and overall width were reduced by 26% and 18% respectively, suggesting a possible role for GH in osteoclastic activity. Serum total insulin-like growth factor-I (IGF-I) concentrations were decreased by 80-90% in both experiments by anti-rGH; these changes were prevented in the first experiment by concurrent treatment with anti-rGH and bGH. The serum IGF-binding protein-3 (IGFBP-3) concentration was also decreased by anti-rGH in experiment 1 (by 86%); the response of the 28-32 kDa IGFBPs was smaller (-35%), and was restored to control values by simultaneous injection of bGH. Western immunoblotting using an antiserum to IGFBP-2 showed that there was a marked decrease from neonatal to adult stages which was independent of anti-rGH treatment. This clearly demonstrated a dissociation of the reciprocal relationship supposed to exist between IGFBPs-2 and -3. The 24 kDa IGFBP-4 was unaffected by anti-rGH but replacement therapy with bGH doubled its concentration. Although the effects on body and muscle weight were prevented when rats were given anti-rGH and bGH simultaneously, the possibility of mediation by other hormones cannot be precluded.

Preliminary characterization of porcine bone marrow stromal cells: skeletogenic potential, colony-forming activity, and response to dexamethasone, transforming growth factor beta, and basic fibroblast growth factor.

Neonatal pig bone marrow stromal cells (PBMSC) were tested in vivo and in vitro to establish their use as a large-animal model for the study of skeletogenesis. When implanted in diffusion chambers in athymic mice for 6-8 weeks, both freshly isolated pig bone marrow and passage 2 PBMSC formed partially mineralized cartilage, bone-like material, and fibrous tissue. The cartilage showed metachromatic, perilacunar staining with toluidine blue and safronin O, alcian blue staining for chondroitin and keratan sulfate, and intense immunostaining for type II collagen. Osteocalcin was immunolocalized to the mineralized regions, consistent with the formation of bone. Alkaline phosphatase was primarily observed in cell layers at boundaries between tissue types. Unstimulated monolayer cultures of PBMSC produced type I but not type II collagen, responded to dexamethasone (10(-8) M) with a 1.7-fold increase in alkaline phosphatase activity, and were stimulated to divide by basic fibroblast growth factor (1.5-fold; EC50 1 ng/ml). Transforming growth factor beta (TGF-beta) blocked both dexamethasone-induced alkaline phosphatase expression (EC50, 1 ng/ml of TGF-beta) and the mitogenic effects of bFGF (EC50 0.06 ng/ml of TGF-beta). When incubated for 10-14 days in medium containing dexamethasone, beta-glycerophosphate and ascorbate PBMSC formed mineralized nodules. Calcification occurred in the middle of the aggregates and was associated with intensely alkaline phosphatase positive cells and a dense type I collagen-rich matrix. PBMSC also displayed colony-forming unit-fibroblastic activity, with approximately 1 in 80 of the plated cells formed colonies > 128 cells over 14-21 days. PBMSC therefore mimic the known activities of stromal cells from other species, including the human, suggesting that they are a valid model for skeletal research.

Visualisation and selective elimination of a subpopulation of mitogen-responsive bone marrow stromal cells using bromodeoxyuridine and photo-induced cell killing.

Porcine bone marrow stromal cells (PBMSC) are a source of skeletogenic mesenchymal progenitor cells. Unfortunately, the heterogeneous nature of these cells in culture complicates the interpretation of their growth-factor responsiveness. We have therefore pulse-labelled mitogen-stimulated PBMSC with bromodeoxyuridine (BrdU) in order to study individual, growth-factor responsive cells in the presence of large numbers of nonresponsive PBMSC. Transfer of growing cells to low serum medium reduced BrdU labelling from 35% to 4% over a period of 24 hours. Subsequent addition of foetal calf serum (FCS) to serum-arrested cultures increased the number of BrdU positive cells to 54% by 16 hours. Addition of basic fibroblast growth factor (bFGF) to serum-arrested cultures induced DNA synthesis in 28% of cell by 16 hours after stimulation. In order to selectively eliminate mitogen responsive cells from mixed cultures, BrdU-substituted cells were photosensitised with bisbenzimide and exposed to bright light. BrdU-labelled PBMSC died within 20-40 hours of bisbenzimide treatment and subsequent illumination, whereas BrdU-labelled cells survived in the dark despite treatment with bisbenzimide. The photokilling procedure appeared to have no long term effect upon the viability of non-BrdU-labelled cells because if subconfluent cells were brought to serum arrest prior to photokilling, no change in DNA content relative to controls was observed after a subsequent 4 or 7 day incubation in Dulbecco's modified Eagle's medium (DMEM)/10% FCS.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone-derived growth factors modulate collagenase and TIMP (tissue inhibitor of metalloproteinases) activity and type I collagen degradation by mouse calvarial osteoblasts.

The finding that osteoblasts synthesize collagenase has led to the hypothesis that bone cells play a major role in bone resorption by degrading the surface osteoid layer, thereby preparing the underlying mineralized bone for osteoclastic action. To further understand the mechanisms regulating osteoid removal, mouse calvarial osteoblasts were cultured on 14C-labelled type I collagen films and the abilities of (i) bovine bone matrix extracts and (ii) purified or recombinant human growth factors, to modify their collagenolytic behaviour were investigated. EDTA/Tris-HCl extracts of bone matrix containing growth factor activity, exerted a dose-dependent inhibition of type I collagenolysis by osteoblasts stimulated with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3, 10 ng/ml). Inhibition was accompanied by a reduction in collagenase activity and an increase in free TIMP (tissue inhibitor of metalloproteinases) in the culture medium. Transforming growth factor-beta, epidermal growth factor, platelet-derived growth factor and the acidic and basic fibroblast growth factors all mimicked these effects. In contrast, insulin-like growth factors-I and -II did not inhibit type I collagenolysis, only partially inhibited collagenase activity, and did not stimulate TIMP production by either 1,25(OH)2D3-treated or untreated cells. These findings provide additional evidence for the tight control exerted on the proteolytic activity of osteoblasts and the importance of TIMP in its regulation. They suggest strongly that the conversion (coupling) of the initial resorptive phase of the bone remodelling cycle to one of deposition, may be mediated by polypeptide growth factors either produced locally by osteoblasts, or released by proteolysis from the bone matrix.

Type I collagen degradation by mouse calvarial osteoblasts stimulated with 1,25-dihydroxyvitamin D-3: evidence for a plasminogen-plasmin-metalloproteinase activation cascade.

To understand the mechanisms regulating osteoid removal by osteoblasts, mouse calvarial osteoblasts were grown on 14C-labelled type I collagen films and stimulated with 1,25-dihydroxyvitamin D-3 (2.5.10(-8) M) for 48-72 h. In the presence of 5% non-inhibitory rabbit serum this resulted in a 2-3-fold increase in collagen degradation and a dramatic change in osteoblast morphology, when compared with untreated osteoblasts. Collagenolysis was accompanied by increased synthesis and release of latent collagenase, gelatinase and stromelysin and a concomitant decrease in their specific inhibitor, TIMP (tissue inhibitor of metalloproteinases). In serum-free medium, osteoblasts failed to degrade collagen, but their ability to lyse collagen could be restored by adding plasminogen (5 micrograms/ml) to the cultures. Plasminogen-dependent collagenolysis was inhibited by human recombinant TIMP (5 units/ml), demonstrating that plasmin, derived from plasminogen, activated latent collagenase and did not itself degrade collagen. Plasminogen activator production was confirmed by culturing osteoblasts on 125I-labelled fibrin plates. Comparison with urokinase-type and tissue-type plasminogen activator standards suggested that osteoblast plasminogen activator was predominantly cell-associated and likely to be of the urokinase type. Immunocytochemistry indicated that osteoblasts also constitutively produce plasminogen activator inhibitor-1. These findings provide evidence for the involvement of a plasminogen-plasmin-latent metalloproteinase activation cascade in type I collagen degradation by osteoblasts, and for its regulation by TIMP and plasminogen activator inhibitor-1.

Degradation of type I collagen films by mouse osteoblasts is stimulated by 1,25 dihydroxyvitamin D3 and inhibited by human recombinant TIMP (tissue inhibitor of metalloproteinases).

Mouse calvarial osteoblasts grown on native type I collagen films degrade collagen in response to 1,25 (OH) 2vitD3. Collagen degradation is accompanied by increased latent collagenase and gelatinase secretion and by a reduction in free TIMP. Exogenous human recombinant TIMP abolished 1,25 (OH) 2vitD3 stimulated collagen degradation and inhibited background collagenolysis. No active metalloproteinases were detectable in the culture medium suggesting sequestration of active enzyme at the site of action or inhibition by residual TIMP. Chondrocytes could not mimic osteoblasts in this system.

Tumor necrosis factors alpha and beta induce osteoblastic cells to stimulate osteoclastic bone resorption.

Antigen- or mitogen-stimulated leukocytes release bone-resorbing activity into culture supernatants in vitro. Among the agents likely to be present in such supernatants are monocyte-derived tumor necrosis factor (TNF-alpha) and lymphocyte-derived tumor necrosis factor (TNF-beta) (lymphotoxin), both of which have recently been shown to stimulate bone resorption in organ culture. To identify the mechanism of action of these agents, we compared bone resorption by isolated osteoclasts with bone resorption by osteoclasts cocultured with osteoblastic cells, and with bone resorption by osteoclasts incubated with supernatants from osteoblastic cells, in the presence and absence of recombinant TNF-alpha and TNF-beta. We found that neither TNF-alpha nor TNF-beta had any significant effect on bone resorption by isolated osteoclasts, but in the presence of osteoblasts the agents caused a twofold to threefold stimulation of bone resorption. A similar degree of stimulation was achieved by supernatants from osteoblasts incubated with TNF before addition to osteoclasts, compared with supernatants to which TNF were added after osteoblast incubation. These experiments suggest that TNF-alpha and TNF-beta stimulate bone resorption through a primary effect on osteoblastic cells, which are induced by TNF to produce a factor that stimulates osteoclastic resorption. Half-maximal stimulation of resorption occurred at 1.5 X 10(-10) M and 2.5 X 10(-10) M for TNF-alpha and TNF-beta, respectively. This degree of potency is comparable to that of parathyroid hormone, the major physiologic systemic regulator of bone resorption, and suggests that the TNF may exert a significant influence on osteoclastic bone resorption in vivo.

Osteoblasts mediate interleukin 1 stimulation of bone resorption by rat osteoclasts.

A monocyte-derived factor with IL-1-like properties has recently been shown to cause resorption of bone in organ culture. We have investigated the action of IL-1 on disaggregated populations of osteoclasts, incubated alone or in the presence of osteoblastic cells, in an attempt to identify the target cell for IL-1 in bone, and to elucidate the mechanism by which IL-1 induces osteoclastic resorption. Osteoclasts were disaggregated from neonatal rat long bones and incubated on slices of human femoral cortical bone. Under these conditions, the majority of osteoclasts form distinctive excavations in the bone surface within 24 h, the volume of which can be quantified by computer-assisted morphometric and stereophotogrammetic techniques. IL-1 had no effect on bone resorption by osteoclasts alone, but when incubated in the presence of calvarial cells or cloned osteosarcoma cells, it induced a 3.8 (+/- 0.38)-fold increase in osteoclastic bone resorption, with significant enhancement at concentrations of greater than or equal to 30 pg/ml. The osteoblastic populations themselves did not resorb bone. The mechanism by which osteoblastic cells stimulate osteoclasts did not appear to depend upon PG synthesis; nor could we detect a diffusible substance in the medium of stimulated cocultures. These results indicate that IL-1 stimulates bone resorption through a primary action on osteoblasts, which are induced by IL-1 to transmit a short-range signal that stimulates osteoclastic bone resorption.