Variations in surgical procedures for hind limb ischaemia mouse models result in differences in collateral formation

OBJECTIVE

To identify the optimal mouse model for hind limb ischaemia, which offers a therapeutic window that is large enough to detect improvements of blood flow recovery, for example, using cell therapies.

MATERIALS AND METHODS

Different surgical approaches were performed: single coagulation of femoral and iliac artery, total excision of femoral artery and double coagulation of femoral and iliac artery. Blood flow restoration was analysed with laser Doppler perfusion imaging (LDPI). Immuno-histochemical stainings, angiography and micro-computed tomography (CT) scans were performed for visualisation of collaterals in the mouse.

RESULTS

Significant differences in flow restoration were observed depending on the surgical procedure. After single coagulation, blood flow already restored 100% in 7 days, in contrast to a significant delayed flow restoration after double coagulation (54% after 28 days, P<0.001). After total excision, blood flow was 100% recovered within 28 days. Compared with total excision, double coagulation displayed more pronounced corkscrew phenotype of the vessels typical for collateral arteries on angiographs.

CONCLUSION

The extent of the arterial injury is associated with different patterns of perfusion restoration. The double coagulation mouse model is, in our hands, the best model for studying new therapeutic approaches as it offers a therapeutic window in which improvements can be monitored efficiently.

Effect of interleukin-17 on nitric oxide production and osteoclastic bone resorption: is there dependency on nuclear factor-kappaB and receptor activator of nuclear factor kappaB (RANK)/RANK ligand signaling?

Interleukin-17 (IL-17) is a proinflammatory cytokine produced exclusively by activated memory T cells and has recently been found to stimulate osteoclastic resorption. Like other proinflammatory cytokines, IL-17 may affect osteoclastic bone resorption indirectly via osteoblasts, possibly by mechanisms previously reported for chondrocytes that respond in very similarly to osteoblasts. As in chondrocytes, but only in combination with tumor necrosis factor-alpha (TNF-alpha), IL-17 induced nitric oxide (NO) production in osteoblastic cells and fetal mouse metatarsals by a nuclear factor-kappaB (NF-kappaB)-dependent mechanism. This effect was associated with elevated mRNA levels of the NF-kappaB isoforms RelA and p50. In fetal mouse metatarsals, IL-17 stimulated osteoclastic bone resorption only in combination with TNF-alpha. The pathway by which the cytokine combination exerts this effect was examined using inhibitors of NO synthesis and NF-kappaB activation. Although both inhibitors used abolished NO production, they did not prevent the stimulatory effect of the cytokine combination on osteoclastic resorption. In contrast, the inhibitors slightly increased osteoclastic resorption, suggesting a suppressive rather than stimulatory effect of NO on cytokine-induced bone resorption. In addition, we showed that IL-17 + TNF-alpha stimulated osteoclastic resorption independent of NF-kappaB signaling. To further examine the pathway by which osteoclastic resorption was stimulated, we used osteoprotegerin, a specific inhibitor of the receptor activator of NF-kappaB (RANK)/receptor activator of the NF-kappaB ligand (RANKL) pathway. Osteoprotegerin partially inhibited IL-17 + TNF-alpha-stimulated osteoclastic resorption only at the high concentration of 1000 ng/mL, whereas it completely blocked parathyroid hormone-related peptide-stimulated resorption at 300 ng/mL. In conclusion, IL-17 stimulated NO production by an NF-kappaB-dependent pathway in osteoblastic cells and fetal mouse metatarsals only in combination with TNF-alpha. Neither NO production nor NF-kappaB signaling, and only partly the RANK/RANKL pathway, were involved in the stimulatory effect of the cytokine combination on osteoblastic bone resorption in these long bones, suggesting the existence of other pathways by which osteoclastic resorption can be stimulated.

Recombinant human extracellular matrix protein 1 inhibits alkaline phosphatase activity and mineralization of mouse embryonic metatarsals in vitro

Two mRNAs are transcribed from the extracellular matrix protein 1 gene (Ecm1): Ecm1a and an alternatively spliced Ecm1b. We studied Ecm1 mRNA expression and localization during endochondral bone formation and investigated the effect of recombinant human (rh) Ecm1a protein on organ cultures of embryonic mouse metatarsals. Of the two transcripts, Ecm1a mRNA was predominantly expressed in fetal metacarpals from day 16 to 19 after gestation. Ecm1 expression was not found in 16- and 17-day-old metatarsals of which the perichondrium was removed. In situ hybridization and immunohistochemistry demonstrated Ecm1 expression in the connective tissues surrounding the developing bones, but not in the cartilage. Biological effects of rhEcm1a protein on fetal metatarsal cultures were biphasic: at low concentrations, Ecm1a stimulated alkaline phosphatase activity and had no effect on mineralization, whereas at higher concentrations, Ecm1a dose dependently inhibited alkaline phosphatase activity and mineralization. These results suggest that Ecm1a acts as a novel negative regulator of endochondral bone formation.

Expression of Indian hedgehog, parathyroid hormone-related protein, and their receptors in the postnatal growth plate of the rat: evidence for a locally acting growth restraining feedback loop after birth

A locally acting growth restraining feedback loop has been identified in the murine embryonic growth plate in which the level of parathyroid hormone-related peptide (PTHrP) expression regulates the pace of chondrocyte differentiation. To date, it is largely unknown whether this feedback loop also regulates the pace of chondrocyte differentiation in the growth plate after birth. We therefore characterized the spatio-temporal expression of Indian hedgehog (IHH), PTHrP, and their receptors in the postnatal growth plate from female and male rats of 1, 4, 7, and 12 weeks of age. These stages are representative for early life and puberty in rats. Using semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) on growth plate tissue, IHH and components of its receptor complex, patched (PTC) and smoothened (SMO), PTHrP and the type I PTH/PTHrP receptor messenger RNA (mRNA) were shown at all ages studied irrespective of gender. Using in situ hybridization, IHH, PTHrP, and PTH/PTHrP receptor mRNA were detected in prehypertrophic and hypertrophic chondrocytes in both sexes during development. In addition, especially in the younger age groups, faint expression of PTH/PTHrP receptor mRNA also was shown in stem cells and proliferative chondrocytes. Immunohistochemistry confirmed the observations made with in situ hybridization, by showing the presence of IHH, PTC, PTHrP, and PTH/PTHrP receptor protein in prehypertrophic and hypertrophic chondrocytes. In addition, staining for hedgehog, PTC, and PTHrP also was observed in growth plate stem cells. No differences in staining patterns were observed between the sexes. Furthermore, no mRNA or protein expression of the mentioned factors was detected in the perichondrium. Our data suggest that in contrast to the proposed feedback loop in the early embryonic growth plate, which requires the presence of the perichondrium, a feedback loop in the postnatal growth plate can be confined to the growth plate itself. In fact, two loops might exist: (1) a loop confined to the transition zone and early hypertrophic chondrocytes, which might in part be autocrine and (2) a loop involving the growth plate stem cells.

Expression of vascular endothelial growth factors and their receptors during osteoblast differentiation

Endochondral bone formation is regulated by systemically and locally acting growth factors. A role for vascular endothelial growth factor (VEGF) in this process has recently been proposed, because inactivation of VEGF inhibits endochondral bone formation via inhibition of angiogenesis. Despite the known effect of VEGF as specific endothelial growth factor, its effects on osteoblast differentiation have not been studied. We, therefore, examined the expression of VEGF-A, -B, -C, and -D and their receptors in a model of osteoblast differentiation using the mouse preosteoblast-like cell line KS483. Early in differentiation, KS483 cells express low levels VEGF-A, -B, and -D messenger RNA, whereas during mineralization, KS483 cells express high levels. In addition, expression of the VEGF receptors, VEGFR1, VEGFR2, and VEGF165R/neuropilin, coincided with expression of their ligands, being maximally expressed during mineralization. VEGF-A production during osteoblast differentiation was stimulated by insulin-like growth factor I that enhances osteoblast differentiation and was inhibited by PTH-related peptide that inhibits osteoblast differentiation. Furthermore, continuous treatment of KS483 cells with recombinant human VEGF-A stimulated nodule formation. Although treatment of KS483 cells with soluble FLT1, an agent that blocks binding of VEGF-A and -B to VEGFR1, did not inhibit nodule formation, this observation does not exclude involvement of VEGFR2 in the regulation of osteoblast differentiation. As it is known that VEGF-A, -C, and -D can act through activation of VEGFR2, other isoforms might compensate for VEGF-A loss. The expression pattern of VEGFs and their receptors shown here suggests that VEGFs play an important role in the regulation of bone remodeling by attracting endothelial cells and osteoclasts and by stimulating osteoblast differentiation.

Oestrogenic compounds modulate cytokine-induced nitric oxide production in mouse osteoblast-like cells

Nitric oxide (NO) is a mediator of bone metabolism with effects on both bone resorption and formation. Its production by both the constitutive and inducible isoforms of nitric oxide synthase (NOS) is affected by oestrogen in several types of cell and in tissues other than bone cells. Recently, oestrogens were found to increase basal NO production by osteoblasts via enhanced activity or expression, or both, of NOS-3. Inflammatory cytokines, however, increase NO by increasing the expression of NOS-2. In this study we have examined whether cytokine-induced NO production by osteoblastic cells was affected by oestrogenic compounds by studying the effect of 17beta-oestradiol and the anti-oestrogens ICI164,384 and 4-hydroxytamoxifen on cytokine-induced NO production in oestrogen receptor positive MC3T3-E1 osteoblast-like cells. Combinations of the inflammatory cytokines interleukin-1beta, tumour necrosis factor-alpha, and interferon-gamma with lipopolysaccharide stimulated NO production up to 11-fold. This cytokine-induced NO production was further increased dose-dependently by the anti-oestrogens ICI164,384 and 4-hydroxytamoxifen (133.3 +/- 3.2% and 146.0 +/- 13.2%, respectively). 17Beta-oestradiol either had no effect on or slightly inhibited cytokine-induced NO production. It did, however, dose-dependently counteract the stimulatory effect of the anti-oestrogens. Concentrations of 17beta-oestradiol needed to prevent the stimulatory effect of 4-hydroxytamoxifen were ca tenfold that of ICI164,384. These findings show that, in addition to the stimulatory effect of oestrogen on basal NO production by NOS-3, cytokine-induced NO production is also affected by oestrogenic compounds in osteoblasts.

A frame-shift mutation in the type I parathyroid hormone (PTH)/PTH-related peptide receptor causing Blomstrand lethal osteochondrodysplasia

Blomstrand osteochondrodysplasia (BOCD) is a rare lethal skeletal dysplasia characterized by accelerated endochondral and intramembranous ossification. Comparison of the characteristics of BOCD with type I PTH/PTH-related peptide (PTHrP) receptor-ablated mice reveals striking similarities that are most prominent in the growth plate. In both cases, the growth plate is reduced in size due to a strongly diminished zone of resting cartilage and the near absence of columnar arrangement of proliferating chondrocytes. This overall similarity suggested that an inactivating mutation of the PTH/PTHrP receptor might be the underlying genetic defect causing BOCD. Indeed, inactivating mutations of the PTH/PTHrP receptor have been recently identified in two cases of BOCD. We describe here a novel inactivating mutation in the PTH/PTHrP receptor. Sequence analysis of all coding exons of the type I PTH/ PTHrP receptor gene and complementary DNA of a case with BOCD identified a homozygous point mutation in exon EL2 in which one nucleotide (G at position 1122) was absent. The mutation was inherited from both parents, supporting the autosomal recessive nature of the disease. The missense mutation resulted in a shift in the open reading frame, leading to a truncated protein that completely diverged from the wild-type sequence after amino acid 364. The mutant receptor, therefore, lacked transmembrane domains 5, 6, and 7; the connecting intra- and extracellular loops; and the cytoplasmic tail. Functional analysis of the mutant receptor in COS-7 cells and of dermal fibroblasts obtained from the case proved that the mutation was indeed inactivating. Neither the transiently transfected COS-7 cells nor the dermal fibroblasts responded to a challenge with PTH or PTHrP with a rise in intracellular cAMP levels, in sharp contrast to control cells. Our results provide further evidence that BOCD is caused by inactivating mutations of the type I PTH/PTHrP receptor and underscore the importance of this receptor in mammalian skeletal development.

Inhibition of terminal chondrocyte differentiation by bone morphogenetic protein 7 (OP-1) in vitro depends on the periarticular region but is independent of parathyroid hormone-related peptide

Bone morphogenetic protein-7, or BMP-7 (OP-1), is highly expressed in the perichondrium of embryonic long bones and is thought to play a role in endochondral ossification. Previously we have shown that BMP-7 inhibits terminal chondrocyte differentiation; that is, chondrocyte hypertrophy and mineralization in cultured explants of embryonic mouse metatarsals. However, the mechanism of this inhibition and the target cells of BMP-7 are still unknown. In this study we show that BMP-7 inhibits terminal chondrocyte differentiation indirectly, via an interaction with the periarticular region of the explants. This region also expresses parathyroid hormone-related peptide (PTHrP). PTHrP regulates terminal chondrocyte differentiation by inhibiting hypertrophic differentiation of prehypertrophic chondrocytes. The differentiating center in turn regulates PTHrP expression via a feedback loop involving Indian hedgehog (Ihh), which is expressed in the prehypertrophic chondrocytes. Ihh is thought to act on perichondrial cells, which in turn start to express an as yet unknown mediator that stimulates PTHrP expression in the periarticular region. It has been suggested that this factor belongs to the BMP-family. We investigated whether the inhibition of terminal chondrocyte differentiation by BMP-7 was due to upregulation of the PTHrP-Ihh feedback loop and whether BMP-7 was the unknown factor in the loop. Here we show that exogenous BMP-7 did not upregulate the mRNA expression of PTHrP, Ihh, or the PTH/PTHrP receptor in cultured wild-type embryonic metatarsals. Furthermore, BMP-7 could still inhibit terminal chondrocyte differentiation in the metatarsals of PTHrP-deficient (PTHrP-/-) mouse embryos. These data indicate that the BMP-7-mediated inhibition of terminal chondrocyte differentiation in vitro is independent of the PTHrP-Ihh feedback loop. We concluded that BMP-7 modulates terminal chondrocyte differentiation and cartilage mineralization of fetal bone explants in vitro via as yet unknown inhibitory factor(s) produced in the periarticular region.

Degradation of extracellular matrix by metastatic follicular thyroid carcinoma cell lines: role of the plasmin activation system

The plasmin activation system plays a key role in extracellular matrix degradation in many malignant tumors. Because no data are available on the involvement of the plasmin activation system in matrix degradation by thyroid carcinoma, the present study was performed using follicular thyroid carcinoma cell lines obtained from a primary tumor (FTC-133) and metastases (FTC-236 and FTC-238) of one patient. Matrix degradation by these cell lines was studied assessing the release of radioactivity from S35-methionine labeled extracellular matrix coated onto plastic. The involvement of constituents of the plasmin activation system as well as matrix metalloproteinases (MMPs), another class of proteolytic enzymes, which can be activated by plasmin, were assessed by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and zymography. In the matrix degradation experiment, S35 release by FTC-133 was significantly higher than FTC-236 and FTC-238. S35 degradation could be inhibited by the plasmin inhibitor aprotinin and by anti-human urokinase-type plasminogen activator (uPA) antibody, indicating the involvement of the plasmin activation system. Matrix degradation could also be inhibited by the MMP inhibitor marimastat, thus demonstrating the involvement of MMPs in matrix degradation by these cell lines. Zymographic assays revealed activity of uPA in all cell lines. However, in contrast with FTC-236 and FTC-238, no plasminogen activator inhibitor (PAI) or PAI1 mRNA were found in FTC-133. Therefore, the differences in PAI activity as observed between the cell lines may originate from differences in PAI1 gene transcription. Differences in PAI1 expression did not affect the attachment of these cell lines to vitronectin. We conclude that the plasmin activation system is involved in extracellular matrix degradation by these metastatic follicular thyroid carcinoma cell lines. Differences in extracellular matrix degradation between the cell lines correspond with differences in PAI1 gene expression, indicating the significance of PAI1 in extracellular matrix degradation by metastatic follicular thyroid carcinoma.

Interleukin-17: A new bone acting cytokine in vitro

Interleukin-17 (IL-17) is a recently cloned cytokine that is exclusively produced by activated T cells, but its receptor has been found on several cells and tissues. Like other proinflammatory cytokines produced by activated T cells, IL-17 may affect osteoclastic resorption and thereby mediate bone destruction accompanying some inflammatory diseases. In the present study, we investigated whether osteogenic cells possess the receptor for IL-17 (IL-17R) and whether IL-17 affects osteoclastic resorption. We found that IL-17R mRNA is expressed both in mouse MC3T3-E1 osteoblastic cells and fetal mouse long bones, suggesting that osteogenic cells may be responsive to IL-17. In fetal mouse long bones, IL-17 had no effect on basal and IL-1beta-stimulated osteoclastic bone resorption, but when given together with tumor necrosis factor-alpha (TNF-alpha) it increased bone resorption dose dependently in serum-free conditions. In addition, IL-17 increased TNF-alpha-induced IL-1alpha, IL-1beta, and IL-6 mRNA expression in fetal mouse metatarsals and IL-1alpha and IL-6 mRNA expression in MC3T3-E1 cells. In conclusion, IL-17R mRNA was expressed by mouse osteoblastic cells and fetal mouse long bones, and IL-17 in combination with TNF-alpha, but not IL-1beta, increased osteoclastic resorption in vitro. IL-17 may therefore affect bone metabolism in pathological conditions characterized by the presence of activated T cells and TNF-alpha production such as rheumatoid arthritis and loosening of bone implants.

Identification of a retinoic acid-inducible element in the murine PTH/PTHrP (parathyroid hormone/parathyroid hormone-related peptide) receptor gene

We have shown previously that the PTH/PTHrP (PTH-related peptide) receptor mRNA becomes expressed very early in murine embryogenesis, i.e. during the formation of extraembryonic endoderm. Retinoic Acid (RA) is a potent inducer of extraembryonic endoderm formation and PTH/PTHrP-receptor expression in embryonal carcinoma (EC) and embryonal stem (ES) cells. Using the P19 EC cell line, we have characterized promoter elements of the murine PTH/PTHrP-receptor gene that are involved in this RA-induced expression. The data show that RA-induced expression of the PTH/ PTHrP-receptor gene is mediated by the downstream P2 promoter. Analysis of promoter reporter constructs in transiently transfected P19 cells treated with RA identified an enhancer region between nucleotides -2714 and -2702 upstream of the P2 transcription start site that is involved in the RA effect. This region matches a consensus hormone response element consisting of a direct repeat with an interspacing of 1 bp (R-DR1). The R-DR1 efficiently binds retinoic acid receptor-alpha (RARalpha)-retinoid X receptor-alpha (RXRalpha) and chicken ovalbumin upstream promoter (COUP)-transcription factor I (TFI)-RXRalpha heterodimers and RXRalpha and COUP-TFI homodimers in a bandshift assay using extracts of transiently transfected COS-7 cells. RA differentiation of P19 EC cells strongly increases protein binding to the R-DR1 in a band-shift assay. This is caused by increased expression of RXR (alpha, beta, or gamma) and by the induction of expression of RARbeta and COUP TFI/TFII, which bind to the R-DR1 as shown by supershifting antibodies. The presence of RXR (alpha, beta, or gamma) in the complexes binding to the R-DR1 suggests that RXR homodimers are involved in RA-induced expression of the PTH/PTHrP-receptor gene. The importance of the R-DR1 for RA-induced expression of PTH/ PTHrP-receptor was shown by an inactivating mutation of the R-DR1, which severely impairs RA-induced expression of PTH/PTHrP-receptor promoter reporter constructs. Since this mutation does not completely abolish RA-induced expression of PTH/PTHrP-receptor promoter reporter constructs, sequences other than the R-DR1 might also be involved in the RA effect. Finally, we show that the RA-responsive promoter region is also able to induce expression of a reporter gene in extraembryonic endoderm of 7.5 day-old transgenic mouse embryos.

Parathyroid hormone-related peptide (PTHrP) induces parietal endoderm formation exclusively via the type I PTH/PTHrP receptor

A number of studies suggest a role for PTHrP and the classical PTH/PTHrP receptor (type I) in one of the first differentiation processes in mouse embryogenesis, i.e. the formation of parietal endoderm (PE). We previously reported that although in type I receptor (-/-) embryos PE formation seemed normal, the embryos were smaller from at least day 9.5 p.c. and 60% had died before day 12.5 p.c. Here we show that the observed growth defect commences even earlier, at day 8.5 p.c. Using two novel antibodies, we show that the expression of the type I receptor protein at this stage is confined to extraembryonic endoderm only. In addition, we show that large amounts of PTHrP protein are present in the adjacent trophoblast giant cells, suggesting a paracrine interaction of PTHrP and the type I PTH/PTHrP receptor in PE formation. The involvement in PE differentiation of other recently described receptors for PTHrP would explain a possible redundancy for the type I receptor in PE formation. However, deletion of the type I PTH/PTHrP receptor in ES cells by homologous recombination completely prevents PTHrP-induced PE differentiation. Based upon these observations, we propose that PTHrP and the type I PTH/PTHrP receptor, although not required for the initial formation of PE, are required for its proper differentiation and/or functioning.

Immunohistochemical investigations on the differentiation marker protein E11 in rat calvaria, calvaria cell culture and the osteoblastic cell line ROS 17/2.8

Until now, many extracellular matrix proteins, e.g. osteopontin and osteonectin, have been used to determine a cell's osteogenic maturation. The disadvantage in evaluation of these proteins is their relative wide-ranging appearance throughout the osteogenic differentiation process. Thus, the aim of this study was to establish an immunohistochemical setup using E11, a marker that binds selectively to cells of the late osteogenic cell lineage. In addition, the histochemical expression of the bone matrix proteins osteonectin, osteopontin and fibronectin was compared to that of E11 using monoclonal antibodies. For light microscopical detection of osteogenic markers in cultured cells we developed a simple paraffin technique using a fibrin glue as embedding medium. This allows the handling of cultured cells such as a tissue sample and includes the use of stored biological specimens for further immunohistochemical experiments. We used newborn rat calvariae for whole tissue preparations and for isolation and cultivation of bone cells. In addition, we included the rat osteosarcoma cell line ROS 17/2.8 in this study. For the first time, we have localised E11 in osteocytes of rat calvaria preparations at the electron microscopical level. E11 was detected at plasma membranes of osteocytes and their processes, but not at those of osteoblasts. Accompanying experiments with cultured newborn rat calvaria cells and ROS 17/2.8 cells revealed E11 reactivity on a subset of cells. The results obtained confirm the suitability of the differentiation marker E11 as a sensitive instrument for the characterisation of bone cell culture systems.

Binding and antiresorptive properties of heterocycle-containing bisphosphonate analogs: structure-activity relationships

To define structure-activity relationships for bisphosphonate activity, we examined the bone binding and antiresorptive properties of heterocycle-containing analogs of risedronate, a pyridylbisphosphonate, in cultures of mouse fetal bone explants. Our studies indicated that hydroxybisphosphonates with the nitrogen molecule in the pyridyl ring were very potent inhibitors of osteoclastic resorption. Changing the place of the nitrogen in the ring structure of risedronate or its methylation did not significantly alter antiresorptive potency in relation to risedronate. Extension of the R2 chain, however, reduced efficacy. In binding experiments, we found that all heterocyclic bisphosphonates with a hydroxyl group in R1 had comparable affinity for bone mineral and inhibited calcium incorporation into bone explants to a similar extent. The affinity of a risedronate analog without R1 was markedly reduced. We also examined the properties of a risedronate analog (NE-10790) belonging to the group of phosphonocarboxylates in which one of the phosphonate groups is substituted by a carboxyl group. NE-10790 had strongly reduced binding affinity, but still retained some antiresorptive activity. Interestingly, the continuous presence of NE-10790 in cultures of fetal mouse metacarpal bones increased its antiresorptive efficacy by about 40-fold compared with 24 h preincubation, whereas, under the same conditions, the potency of high-affinity hydroxybisphosphonates did not change or only slightly increased. This may be explained by the differences in pharmacokinetic behavior between compounds of high and of low affinity for bone mineral. These data show that, as with alkylbisphosphonates, heterocycle-containing bisphosphonates with a nitrogen functionality in the R2 chain are potent antiresorptive agents and a hydroxyl substitution in the R1 chain confers high affinity for bone mineral, probably due to tridentate configuration. The group of phosphonocarboxylates, with strongly reduced bone affinity, provides an interesting therapeutic option.

Plasma nitrate+nitrite levels are regulated by ovarian steroids but do not correlate with trabecular bone mineral density in rats

Nitric oxide (NO) is a mediator of bone metabolism and its production is under the control of gender hormones in several cell types or tissues. Changes in endogenous NO production, measured as plasma nitrate+nitrite levels, may therefore contribute to ovariectomy (OVX)-induced bone loss. We studied plasma nitrate+nitrite levels and trabecular bone mineral density (TBMD) 4 weeks after sham-operation or OVX in rats receiving various hormonal treatments. OVX decreased plasma nitrate+nitrite levels significantly and this was accompanied by a significant decrease in TBMD. Treatment with oral ethinyl oestradiol (EE) and subcutaneous 17beta-oestradiol dose-dependently prevented the decrease in plasma nitrate+nitrite levels after OVX, but treatment with oral 17beta-oestradiol did not. Oestrogen treatment, 17beta-oestradiol (s. c. or orally) or EE (orally), prevented the OVX-induced decrease in TBMD. Treatment of sham-operated rats with the anti-oestrogen ICI164, 384 induced a significant decrease in TBMD that corresponded to 54% of the decrease observed after OVX, but did not affect plasma nitrate+nitrite levels. Treatment of ovariectomized rats with Org 2058, a pure progestagen, did not prevent bone loss, but prevented the decrease in plasma nitrate+nitrite levels dose-dependently. Treatment with tibolone, a synthetic steroid with combined weak oestrogenic, progestagenic, and androgenic properties, or with progestagen in combination with EE completely prevented bone loss after OVX. These treatments, however, only partly prevented the OVX-induced decrease in plasma nitrate+nitrite levels. In conclusion, OVX decreased both TBMD and plasma nitrate+nitrite levels. Although plasma nitrate+nitrite levels were under the control of both oestrogen and progesterone, TBMD was affected by oestrogen only. Decreased systemic production of NO is, therefore, not involved in OVX-induced bone loss in rats.

Role of astrocyte-derived tissue-type plasminogen activator in the regulation of endotoxin-stimulated nitric oxide production by microglial cells

In mixed glial cell cultures from cerebral cortices of newborn rats, endotoxin induces nitric oxide (NO) production in microglial cells. Earlier we demonstrated that endotoxin induced NO production by microglial cells is inhibited in the presence of astroglial cells by transforming growth factor beta (TGFbeta). Both microglial and astroglial cells produce TGFbeta in a biologically inactive form, which can be activated by plasmin generated by plasminogen activators (PA). In the present paper we describe studies on the mechanism by which glial cells may activate inactive TGFbeta and its potential inhibitory effect on NO production by microglial cells. Inhibition of plasmin increased NO production in endotoxin-treated mixed glial cell cultures. Subsequently, antibodies against tissue-type plasminogen activator (tPA) increased NO production in endotoxin-treated mixed glial cell cultures while amiloride, an inhibitor for urokinase (uPA), had no effect. We hereby concluded that tPA is the crucial PA involved in plasmin production resulting in inhibition of NO production in mixed glial cell cultures. Zymography and Northern blot analysis of purified astroglial, microglial, and mixed glial cell cultures demonstrated that astroglial cells produce tPA and a plasminogen activator inhibitor (PAI-1) and are thereby responsible for the production of plasmin which may activate the inactive TGF in these cultures. In conclusion, astroglial-derived tPA plays a major role in the inhibition of NO production by endotoxin-treated microglial cells through enhanced plasmin production and possible subsequent TGFbeta activation.

IL-1alpha, IL-1beta, IL-6, and TNF-alpha steady-state mRNA levels analyzed by reverse transcription-competitive PCR in bone marrow of gonadectomized mice

Loss of gonadal function in both females and males is associated with increased rates of bone loss by a yet unidentified mechanism. There is ample evidence that cytokines that are produced in the bone microenvironment and stimulate the activity and/or formation of osteoclasts are involved. In the present study, we examined whether gonadectomy increases cytokine production via increased transcription in the bone marrow of mice. For this, the in vivo steady-state mRNA levels of multiple cytokines were determined in the central bone marrow compartment of mice at different time points following ovariectomy or orchidectomy by reverse transcription-competitive polymerase chain reaction. The limit of detectable differences in mRNA expression was approximately 2-fold. Bone marrow mRNA levels of the cytokines interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were elevated up to 30-fold after treatment of mice with lipopolysaccharide. Following gonadectomy, there were no differences in the mRNA expression of these cytokines in bone marrow of female and male mice 4, 7, and 14 days after surgery. Gender steroid deficiency does not, therefore, increase steady-state mRNA levels of IL-1alpha, IL-1beta, IL-6, and TNF-alpha in cells of the central bone marrow compartment in mice. If changes have occurred these should have been less than 2-fold or in a small cell population. These results do not preclude an important role of these cytokines in the induction of bone loss after gonadectomy. For example, bone marrow cells situated close to the bone surface or bone cells may be responsible for increased cytokine synthesis. Alternatively, the loss of gender steroids may alter post-transcriptional events in cytokine synthesis and activity or may modify the responsiveness of target cells.

Differential effects of aminosubstituted analogs of hydroxy bisphosphonates on the growth of Dictyostelium discoideum

Replacing the hydroxyl group in the bone-binding site of three clinically useful bisphosphonates (etidronate, pamidronate, and olpadronate) by an amino group resulted in great differences in their antiresorptive potencies in vitro. In the present study, this is also shown in vivo in mice treated with the six bisphosphonates at doses of up to 16 microM/kg/day for 12 days. Because binding to bone mineral is nearly the same for all tested bisphosphonates, these findings suggest that the aminosubstitution affects the cellular action of the bisphosphonates. This was tested in the cellular slime mould Dictyostelium discoideum in which cellular effects of bisphosphonates can be examined independently of binding to bone mineral. Etidronate and its aminosubstituted analog were equipotent in inhibiting amebal growth, while pamidronate was somewhat more potent than its analog. Whereas olpadronate was a potent inhibitor of axenic growth of Dictyostelium amebae, the aminosubstitution reduced its potency drastically (IC50 12 microM and 700 microM, respectively). The similarities between the inhibitory effects of the bisphosphonates tested on bone resorption in vitro and in vivo and on the growth of Dictyostelium amebae confirm that the differences in antiresorptive potencies found reflect differences in cellular effects and suggest that bisphosphonates may bind to more than one intracellular target.

Role of integrins in the attachment of metastatic follicular thyroid carcinoma cell lines to bone

One of the principle targets for metastasis of follicular thyroid carcinoma (FTC) is the skeleton. Because no data are available on the role of the integrin adhesion molecule family in the attachment of FTC to bone, we studied the attachment characteristics of three FTC cell lines to bone and the role of integrins. Three cell lines were used from the same patient, one (FTC-133) from the primary tumor and two (FTC-236 and FTC-238) from metastases. Attachment of FTC cell lines to bone was assessed on conditioned medium of an osteoblastic cell line, coated onto plastic, as an in vitro model of bone matrix. The synthetic RGD (Arg-Gly-Asp) peptide GRGDS impaired attachment of the FTC cell lines to bone matrix, demonstrating the role of integrins in the attachment of FTC to bone. Attachment of FTC-133 to bone matrix was blocked completely by GRGDS, whereas attachment of FTC-236 and FTC-238 could not be impaired completely. Semiquantitative polymerase chain reaction (PCR) of cDNA from the cell lines indicated stronger expression of alpha5 integrin mRNA in FTC-133 than in the other cell lines. In line with this, attachment of FTC-133 to bone matrix could be inhibited almost completely by anti alpha5 and beta1 integrin antibodies, indicating the importance of the fibronectin receptor in the attachment of FTC-133 to bone. Binding of FTC-236 and FTC-238 to bone matrix could not be inhibited completely by anti-integrin antibodies, suggesting an additional role of nonintegrin adhesion molecules in the attachment of FTC-236 and FTC-238 to bone. The synthetic bone sialoprotein cyclic peptide, CNB, revealed antiadhesive effects in the binding of FTC to bone. In conclusion, integrins play an important role in the attachment of metastatic FTC to bone. Differences in the functional involvement of integrins in the attachment to bone are observed between the three cell lines studied. From the present results, antiadhesive interventions with synthetic RGD peptides in FTC may be designed.

Differential expression of estrogen receptors alpha and beta mRNA during differentiation of human osteoblast SV-HFO cells

Estrogens have been shown to be essential for maintaining a sufficiently high bone mineral density and ER alpha expression has been demonstrated in bone cells. Recently, a novel estrogen receptor, estrogen receptor beta (ERbeta) has been identified. Here we demonstrate that also ERbeta is expressed in human osteoblasts, and that ER alpha and ERbeta are differentially expressed during human osteoblast differentiation. ERbeta mRNA expression increased gradually during osteoblast culture, resulting in an average increase of 9.9+/-5.3 fold (mean+/-S.D., n=3) at day 21 (mineralization phase) as compared to day 6 (proliferation phase). In contrast, ER alpha mRNA expression levels increased only slightly until day 10 (2.3+/-1.7 fold) and then remained constant. The observed differential regulation of ER alpha and beta is suggestive for an additional functional role of ERbeta to ER alpha in bone metabolism.

Expression of the parathyroid hormone-related peptide gene in retinoic acid-induced differentiation: involvement of ETS and Sp1

Differentiation of P19 embryonal carcinoma (EC) and embryonal stem (ES)-5 cells with retinoic acid (RA) induces expression of PTH-related peptide (PTHrP) mRNA. In this study we have characterized a region between nucleotide (nt) -88 and -58 relative to the transcription start site in the murine PTHrP gene that was involved in this expression. Sequence analysis identified two partially overlapping binding sites for the Ets family of transcription factors and an inverted Sp1-binding site. Two major specific bands were detected in a bandshift assay using an oligonucleotide spanning nt -88 and -58 as a probe and nuclear extracts from both undifferentiated and RA-differentiated P19 EC cells. The lower complex consisted of Ets-binding proteins as demonstrated by competition with consensus Ets-binding sites, while the upper complex contained Sp1-binding activity as demonstrated by competition with consensus Sp1-binding sites. The observed bandshift patterns using nuclear extracts of undifferentiated or RA-differentiated P19 cells were indistinguishable, suggesting that the differentiation-mediated expression was not caused by the induction of expression of new transcription factors. Mutations in either of the Ets-binding sites or the Sp1-binding site completely abolished RA-induced expression of PTHrP promoter reporter constructs, indicating that the RA effect was dependent on the simultaneous action of both Ets- and Sp1-like activities. Furthermore, these mutations also abolished promoter activity in cells that constitutively expressed PTHrP mRNA, suggesting a central role for the Ets and Sp1 families of transcription factors in the expression regulation of the mouse PTHrP gene.

The role of interleukin-6 in the induction of hypercalcemia in renal cell carcinoma transplanted into nude mice

Hypercalcemia is a well known complication of renal cell carcinoma (RCC). As RCCs can produce IL-6, and IL-6 may stimulate bone resorption and cause mild hypercalcemia, we examined whether IL-6 is involved in renal cancer-associated hypercalcemia in vivo. Three human renal cell carcinoma tumor lines (RC-8, RC-9, and NC-65) growing in nude mice were studied. Tumors were implanted s.c., and parameters of bone metabolism and serum human IL-6 levels were determined in relation to tumor volume (TV). All three tumor lines secreted human IL-6, although in different quantities. The maximum level of IL-6 in RC-8 was 434 pg/ml (TV, 200 mm3), that in RC-9 was 81 pg/ml (TV, 1800 mm3), and that in NC-65 was 2368 pg/ml (TV, 1800 mm3). Hypercalcemia developed in RC-8 and RC-9 tumor-bearing animals, but not in NC-65-bearing animals. The hypercalcemia in both RC-8 and RC-9 tumor lines was associated with elevated levels of PTH-related peptide (PTHrP) and loss of trabecular bone volume. Serum calcium and phosphate concentrations showed an almost linear relationship with plasma PTHrP independently of the tumor line and serum IL-6 levels. No hypercalcemia occurred in the NC-65 animals, which had the highest levels of IL-6, but no detectable plasma PTHrP and PTHrP messenger RNA expression in the tumor. Administration of neutralizing antibodies to IL-6 to RC-8 animals normalized serum calcium concentrations and PTHrP values and induced a significant inhibition of tumor growth. No such effect on tumor growth of anti-IL-6 was seen in the other two tumor lines. The normalization of serum calcium in RC-8 mice is most likely attributed to the growth-inhibiting effect of anti-IL-6 on RC-8 tumor. We conclude that IL-6 secreted by RCC does not contribute directly to hypercalcemia, but may enhance hypercalcemia by stimulating the tumor growth of a subpopulation of PTHrP-secreting carcinomas.

Effect of alendronate treatment on the osteoclastogenic potential of bone marrow cells in mice

Bisphosphonates suppress bone resorption by inhibiting the activity of mature osteoclasts as well as the formation of osteoclasts from bone marrow-derived precursor cells. It is not yet known at which level of osteoclast development this latter action is exerted and whether this is due to a systemic effect of circulating bisphosphonate or to an action at the bone surface, given the property of these compounds to concentrate specifically at active bone sites. We addressed these questions in an ex vivo study in mice. The animals were treated with the bisphosphonate alendronate for various periods, and the central compartment of the bone marrow was isolated and cultured together with osteoclast-free fetal mouse bone explants. In this way the capacity of bone marrow cells, exposed previously to alendronate in vivo, to generate osteoclasts and induce resorption in vitro was examined. Alendronate (0.25 mg/kg, subcutaneously) given to mice for periods up to 4 weeks suppressed bone resorption, as expected, but did not affect the capacity of bone marrow cells to develop into mature osteoclasts and resorb the calcified matrix of bone explants. In addition, using monoclonal antibodies specific for different macrophage-granulocyte precursor subsets, we found that alendronate treatment did not affect the pattern of antigen expression of bone marrow cells, which is in line with the lack of an effect of the bisphosphonate on the ability of bone marrow cells to induce resorption in vitro. In contrast, in control experiments, lipopolysaccharide (0.1 mg) treatment induced marked changes in the pattern of antigen expression of bone marrow cells. In conclusion, our studies demonstrate that the inhibition of bone resorption by alendronate does not involve alteration of the osteoclastogenic potential of osteoclast progenitors (precursors) from the central bone marrow compartment. Moreover, this treatment did not alter the expression of markers specific for monocyte-macrophage precursors as well as mature macrophages. These results suggest that the effects of alendronate are exerted at the bone surface at late osteoclast precursors (and mature osteoclasts).

Bone matrix degradation by the plasminogen activation system. Possible mechanism of bone destruction in arthritis

The observed increase in urokinase-type plasminogen activator (u-PA) and its receptor (u-PAR) in synovial tissue of patients with rheumatoid arthritis (RA) suggests pathophysiological involvement of the plasminogen activation (PA) system in inflammatory joint disease. In the present study, we investigated the capacity of the PA system to degrade non-mineralized and mineralized bone-like matrix in vitro as a model for bone destruction. Transfected mouse LB6 cell lines, that expressed either human u-PA or u-PAR, were cultured separately and simultaneously on radiolabelled bone matrix in the presence of plasminogen. Osteoblast-like murine calvarial MC3T3-E1 cells were used to produce a well-characterized, highly organized bone-like matrix, that could be mineralized in the presence of beta-glycerol phosphate. Bone matrix degradation was followed by the release of radioactivity in the culture medium. u-PA-producing cells, in contrast to u-PAR-producing cells, degraded both non-mineralized and mineralized bone matrix. This effect could be inhibited by anti-u-PA antibodies, as well as by tranexamic acid and by aprotinin, indicating that the degrading activity is u-PA mediated and plasmin dependent. Co-cultivation of a small portion of u-PA-producing cells with u-PAR-expressing cells resulted in a marked increase in degradation activity. Reduction of this potentiating effect by suramin or the amino-terminal fragment of u-PA, both competitive inhibitors of u-PA receptor binding, shows that this synergistic effect is due to binding of u-PA to u-PAR. u-PAR must be cell associated, as binding of u-PA to a soluble u-PAR prevented this enhancement. The capability of the PA system to degrade bone matrix in vitro, and the previously demonstrated increased expression of u-PA and u-PAR in synovial tissue of patients with RA, further support a role for the PA system in the development of bone erosions.

Differential effects of angiotensin II and transforming growth factor beta on the production of heparan sulfate proteoglycan by mesangial cells in vitro

This study approaches the question of whether angiotensin II (AngII) and transforming growth factor beta (TGF-beta) are important mediators for mesangial heparan sulfate proteoglycan (HSPG) production. This might explain the beneficial effects of angiotensin-converting enzyme inhibitors observed in several kidney diseases independent from their hemodynamic effects. Metabolic-labeling studies revealed that AngII induced a decrease of HSPG synthesis with decreases in N-sulfation of the glycosaminoglycan side chains. ELISA measurements with a heparan sulfate (HS)-specific monoclonal antibody confirmed that AngII decreased HS production. AngII increased TGF-beta production in a dose-dependent fashion. Specific mRNA for the large basement membrane HSPG (perlecan) decreased, whereas mRNA for TGF-beta increased after incubation with AngII. Blockade of the Subtype 1 Ang-II receptor (ATR1) reversed both the effects of AngII on HSPG and TGF-beta production. Coincubation of the mesangial cells with neutralizing antibodies against TGF-beta significantly reduced the production of HS as compared with control and AngII. These results indicate that the decrease in HS synthesis induced by AngII is not mediated by an increase in TGF-beta, but on the contrary, the increase in TGF-beta partially counteracts the inhibition of HS production by AngII. Considering the important role of HSPG in maintaining the glomerular charge barrier, cell proliferation, and matrix interaction, downregulation of the production of this molecule by increased local AngII concentrations could have important consequences, such as albuminuria and matrix expansion.

Role of fibroblasts in the regulation of proinflammatory interleukin IL-1, IL-6 and IL-8 levels induced by keratinocyte-derived IL-1

In the epidermis, the keratinocytes are the first cells to be encountered by external stimuli and they are able to promote the inflammatory response by increased production and release of various cytokines. In their turn, these cytokines may directly affect the production of proinflammatory cytokines in human dermal fibroblasts. In addition, in both epithelial and mesenchymal cells cytokine production may be modulated by their mutual interaction, and thereby regulate the inflammatory response. The present study aimed to examine the role of fibroblasts in the regulation of proinflammatory IL-1, IL-6 and IL-8 levels induced by keratinocyte-derived IL-1. The data show that in fibroblasts exposed to conditioned media derived from cultures of normal human keratinocytes or squamous carcinoma cells (SCC-4), both the IL-8 and IL-6 mRNA expression as well as protein production were elevated. In addition, it was shown that these effects were induced by IL-1 alpha. The IL-1 alpha-induced increase in IL-8 and IL-6 production, both on the protein level as well as on the mRNA level, were concentration dependent and occurred almost simultaneously. While the induction of IL-6 and IL-8 occurred simultaneously, the IL-6 mRNA remained elevated for longer. In contrast to increased IL-6 and IL-8 production the IL-1 alpha levels markedly decreased upon culturing of fibroblasts in keratinocyte-derived conditioned medium. From internalization experiments it could be concluded that binding of IL-1 to IL-1 receptors, and its subsequent internalization and intracellular degradation is the most likely mechanism involved in the reduction of IL-1 levels by fibroblasts. Comparing the rate of IL-1 reduction in the presence of various cell types indicated that the rate of IL-1 reduction is directly related to the number of IL-1 receptors found on these cell types. In conclusion, these results indicate that the release of IL-1 alpha by activated keratinocytes may act as an inducer of IL-8 and IL-6 production in neighbouring fibroblasts. This may be an important pathway for the amplification of the inflammatory response. The amounts of both cytokines produced by fibroblasts were at least two to three orders of magnitude higher than those produced by keratinocytes, suggesting an important role of fibroblasts in the general inflammatory response. Furthermore, fibroblasts might be involved in turning off this inflammatory response by reducing IL-1 levels, most likely via IL-1 receptor-mediated uptake.

Parathyroid hormone related protein and interleukin-6 mRNA expression in larynx and renal cell carcinomas from normocalcaemic and hypercalcaemic patients

AIMS

To determine the expression of parathyroid hormone related protein (PTHrP) and interleukin-6 (IL-6) mRNAs and their possible relation in malignant tumours, derived from patients with and without hypercalcaemia, commonly associated with humoral hypercalcaemia of malignancy.

METHODS

PTHrP and IL-6 mRNA expression was studied by northern blot analysis in tumour specimens from 13 consecutive patients. Six patients (two with hypercalcaemia) had squamous cell carcinomas of the larynx and seven (one with hypercalcaemia) had renal cell carcinomas.

RESULTS

There was no relation between the histological features of the tumours and the expression of either PTHrP or IL-6 mRNAs. PTHrP mRNA was detected in all squamous cell carcinomas, expression being highest in the two patients with hypercalcaemia. In the renal cell carcinomas PTHrP mRNA was expressed only in the patient with hypercalcaemia. IL-6 mRNA was detected in nearly all tumours studied but there was no apparent relation between its expression and that of PTHrP mRNA or serum calcium concentrations.

CONCLUSIONS

PTHrP mRNA expression is increased in patients with hypercalcaemia but is not related to IL-6 mRNA expression. The results suggest a quantitative relation between PTHrP gene expression and hypercalcaemia, and imply that different mechanisms account for this expression in squamous and renal cell carcinomas.

Regulation of plasminogen activation, matrix metalloproteinases and urokinase-type plasminogen activator-mediated extracellular matrix degradation in human osteosarcoma cell line MG63 by interleukin-1 alpha

Plasmin-mediated extracellular proteolysis has been implicated in the degradation of bone in normal and pathological conditions. Normal and malignant osteoblasts can produce both tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). We have used the osteosarcoma cell line MG63 to address the question of whether the enhanced bone turnover in osteosarcomas is mediated by t-PA or by u-PAA and to study the effect of the cytokine interleukin-1 alpha (IL-1 alpha), known to influence bone degradation, on the plasminogen activator production and extracellular matrix degradation in malignant osteoblastic cells. Furthermore, the effect of IL-1 alpha on the synthesis of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) was analyzed. u-PA production by MG63 was high (approximately 180 ng/10(6) cells/24 h). Also t-PA and PAI-1 production was observed. u-PA production was rapidly increased in MG63 by IL-1 alpha (10 ng/ml), whereas an effect on t-PA production was only found after a prolonged incubation and hardly any effect of IL-1 alpha on PAI-1 production was observed. mRNA analysis revealed similar effects. u-PA receptor (u-PAR) mRNA was detectable in MG63 cells and could be increased by IL-1 alpha after 24 h. In MG63, u-PA-mediated extracellular matrix degradation was detectable, and IL-1 alpha increased the u-PA-mediated matrix degradation (approximately 2-fold). Under control conditions in MG63, only MMP-2, TIMP-1, and TIMP-2 mRNA could be observed. After the addition of IL-1 alpha, a very rapid increase in MMP-1 and MMP-3 mRNA could be observed as well as a moderate increase in TIMP-1 mRNA. The presence of MMP-2 was demonstrated by gelatin zymography. These results show that IL-1 alpha can stimulate u-PA production and can regulate extracellular proteolytic activity mainly via u-PA induction in the MG63 osteosarcoma cell line. Furthermore, IL-1 alpha has a strong stimulating effect on the production of MMP-1 and MMP-3. These findings suggest that u-PA and possibly MMP-1 and MMP-3 play an important role in the process of bone turnover in osteosarcomas.

Interleukin-6 and the acute phase response during treatment of patients with Paget's disease with the nitrogen-containing bisphosphonate dimethylaminohydroxypropylidene bisphosphonate

Bisphosphonates suppress bone resorption and are used in the management of bone diseases with increasing frequency. In some patients treated for the first time with potent nitrogen-containing bisphosphonates, there is a transient febrile reaction and transient hematological changes suggestive of an acute phase response. Because IL-6 is considered to be an important mediator of the acute phase response, we examined the changes in circulating IL-6 bioactivity in 38 patients with Paget's disease treated with the nitrogen-containing bisphosphonate (3-dimethyl-amino-1-hydroxypropylidene)-1,1-bisphosphonate (dimethyl-APD). 16 patients who had never received such bisphosphonate were treated with oral dimethyl-APD (100-400 mg/day) and 22 (9 for the first time) with intravenous dimethyl-APD 4 mg/day. Treatment was given for 10 days. Eleven of 38 patients, all first treatments, showed an increase in body temperature of more than 0.5 degrees C exceeding 37 degrees C associated with a significant decrease in lymphocyte count and an increase in serum CRP values. These changes were transient and did not occur in the patients with no febrile response. In patients with a febrile reaction circulating IL-6 bioactivity increased significantly and this increase generally preceeded the rise in temperature. Moreover, patients with an acute phase response had significantly higher peak IL-6 values than those without (128 +/- 30 vs. 31 +/- 4 U/ml, p < 0.001). The peaks in plasma IL-6 were further correlated with the peaks in temperature and in serum CRP values (r = 0.49, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of plasminogen activation in normal keratinocytes and SCC-4 cells by fibroblasts

The plasminogen activator (PA)/plasmin system is thought to be involved in processes such as tumor invasion and wound healing, during which epithelial and mesenchymal cells come close together. However, information on regulation of the PA/plasmin system during epithelial-mesenchymal interactions is scarce. Therefore, we examined the in vitro modulation of the production and activity of the components of the PA/plasmin system in squamous carcinoma cells (SCC-4) and normal human keratinocytes in relation to cell density and the presence or absence of fibroblasts (3T3 cells). There was an inverse relation between cell density and mRNA expression for urokinase-type plasminogen activator (u-PA) and u-PA receptor in both SCC-4 cells and keratinocytes. In addition, such a relation was found for plasminogen activator inhibitor types 1 (PAI-1) and 2 (PAI-2) in SCC-4 monocultures, but not in keratinocyte monocultures. In contrast to monocultures, variation of cell density did not affect the mRNA expression of the components of the PA/plasmin system in cocultures of SCC-4 cells or keratinocytes with 3T3 cells. However, the relative expression of mRNAs in co-cultures was clearly different from that in monocultures, especially at low cell density. For most of the components of the PA/plasmin system, a decrease in mRNA expression and u-PA receptor protein was observed at most cell densities, whereas for PAI-1 only in keratinocytes a marked increase was documented. Zymography of supernatants revealed that the levels of both free u-PA and PA-PAI were increased in SCC-4/3T3 co-cultures, whereas in keratinocytes/3T3 co-cultures, only levels of the PA-PAI complex were increased, while the amount of free u-PA activity decreased. This occurred despite the increase u-PA immunoreactivity and was probably caused by the markedly elevated levels of immunoreactive PAI-1. The results of the present study reveal that the production and synthesis of various components of the PA/plasmin system in keratinocytes and SCC-4 cells depend on the density of epithelial cells and are modulated by fibroblasts, probably through a direct cell-cell or cell-matrix contact. Fibroblast-induced modulations are similar in keratinocytes and SCC-4 cells except for the regulation of PAI-1, which is markedly enhanced only in keratinocytes. This suggests that the modulation of PA activity in the direct microenvironment may be different under physiologic and pathologic conditions.

Inducible production of nitric oxide in osteoblast-like cells and in fetal mouse bone explants is associated with suppression of osteoclastic bone resorption

Nitric oxide (NO) has been suggested to be involved in the regulation of osteoclast activity. Since osteoblasts, through the release of various factors, are the main regulators of osteoclastic resorption, first we have investigated whether osteoblast-like cells and fetal mouse long bone explants are able to produce NO. Second, we have assessed the effect of NO on osteoclastic resorption in whole bone cultures. In this study we show that primary rat osteoblast-like cells as well as the clonal rat osteoblast-like cell line UMR-106, stimulated with IFN-gamma together with TNF-alpha and LPS, produce NO, measured as nitrite production. IL-1 alpha enhanced while TGF-beta 2 inhibited TNF-alpha + IFN-gamma + LPS-stimulated NO production in UMR-106 cells dose dependently. Both the cytokines, however, had no effect when given alone. The competitive inhibitor of NO production, NG-monomethyl-arginine (L-NMMA), and cycloheximide abolished the increase in nitrite production induced by TNF-alpha + IFN-gamma + LPS, while hydrocortisone had no effect, as previously reported for chondrocytes. Calciotropic hormones had either no effect [1,25(OH)2D3] or had a small inhibitory effect (parathyroid hormone) on stimulated NO production. Furthermore, we found that in cultured fetal mouse long bone explants the combination of TNF-alpha + IFN-gamma + LPS as well as the NO donor sodium nitroprusside could inhibit osteoclastic resorption, measured as 45Ca release. The inhibition of resorption was prevented by concurrent administration of L-NMMA. Histological evaluation revealed that the TNF-alpha + IFN-gamma + LPS-induced inhibition of 45Ca release was associated with a decrease in the number of tartrate-resistant acid phosphatase-positive osteoclasts. We propose that the NO production by osteogenic cells (osteoblasts and chondrocytes) may represent an important regulatory mechanism of osteoclastic activity especially under pathological conditions characterized by release of bone-resorbing inflammatory cytokines.

Removal of hematopoietic cells and macrophages from mouse bone marrow cultures: isolation of fibroblastlike stromal cells

A method is described that permits the removal of hematopoietic cells and macrophages from mouse bone marrow cultures. The method is based on the difference in effect of extracellular ATP4- ions (ATP in the absence of divalent, complexing cations) on cells of hematopoietic origin, including macrophages, and of nonhematopoietic origin, such as fibroblastlike stromal cells. In contrast to fibroblastlike cells, hematopoietic cells and macrophages form under the influence of ATP4- lesions in their plasma membranes, which allows the entrance of molecules such as ethidium bromide (EB) and potassium thiocyanate (KSCN), which normally do not easily cross the membrane. The lesions can be rapidly closed by the addition of Mg2+ to the incubation medium, leaving the EB or KSCN trapped in the cell. This method allows the selective introduction of cell-toxic substances such as KSCN into hematopoietic cells and macrophages. By using this method, fibroblastlike stromal cells can be isolated from mouse bone marrow cultures.

Use of a rat model for the simultaneous assessment of pharmacokinetic and pharmacodynamic aspects of bisphosphonate treatment: application to the study of intravenous 14C-labeled 1-hydroxy-3-(1-pyrrolidinyl)-propylidene-1,1-bisphosphonate

Bisphosphonates are drugs that suppress osteoclast-mediated bone resorption and are used with increasing frequency in the treatment of skeletal disorders. Therapeutic regimens are largely based on pharmacodynamic information because of difficulties in obtaining and interpreting pharmacokinetic data. We describe here the application of a permanently cannulated rat model, previously used in other areas of endocrine research, to the simultaneous study of pharmacokinetic and pharmacodynamic properties of the newly developed bisphosphonate EB-1053 [1-hydroxy-3-(1-pyrrolidinyl)propylidene-1,1-bisphosphonate]. Two groups of five rats each received daily intravenous injections of [14C]EB-1053 (0.025 and 0.1 mg/day, respectively); a third group (n = 7) received only normal saline injections and served as control. Treatment was given for at least 20 days. A fourth group (n = 3) received IV injections of the bisphosphonate on three separate occasions. Following IV administration, EB-1053 was rapidly cleared from the circulation. Urinary excretion of radioactivity reached about 55% of the daily administered dose within 48 h and remained at this level during the whole treatment period, indicating continuing retention of the bisphosphonate. Bone resorption, assessed biochemically as the hydroxyproline to creatinine ratio in urine, was suppressed effectively with both doses used. Suppression reached a maximum around day 4 and remained at the same level until the end of treatment. Accumulation of the bisphosphonate in the skeleton was therefore not associated with a cumulative effect on bone resorption. This strongly suggests that in treatment planning a distinction should be made between surface-bound and hence biologically active bisphosphonate from the drug which is incorporated in bone during bone turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor growth delay by laser-generated shock waves

The antiproliferative effect of laser-generated shock waves (L-SW) was investigated on a human renal cell carcinoma, RC-8, grown subcutaneously in the nu/nu mouse. The RC-8 is characterized by the syndrome of humoral hypercalcemia of malignancy (HHM) associated with profound cachexia, increase of serum Ca level, hypophosphatemia, and an enhancement of serum parathyroid-like peptides. In this model system, the effects on cachexia and tumor growth were studied after a series of pulses (3-200) generated by a Candela LFDL/3 equipped pulsed-dye laser with optical fiber guided through a hypodermic needle with a 45 degrees angle bended tip, stuck through the skin of the mouse, and positioned directly below the tumor. The antitumor effect, expressed as a delay of tumor growth, was found to be dependent on number of pulses applied, tumor size, and growth rate (alpha). Treatment of RC-8 with alpha = 0.21 was effective only after 200 pulses combined with a tumor volume smaller than 100 mm3. Under these conditions a growth delay of approximately 8 days was observed, paralleled by delay of animal weight loss (cachexia). Under conditions of a decreased growth rate of RC-8 (alpha = 0.13), the susceptibility toward L-SW was found to be increased, expressed by a suppression of tumor growth after 100 pulses. However, no L-SW-associated delay of cachexia was observed under these latter conditions.

Quantification of adherent and nonadherent cells cultured in 96-well plates using the supravital stain neutral red

In this study we present a rapid, simple, sensitive, inexpensive, and environment-friendly assay for determination of the number of adherent or nonadherent cells cultured in 96-well plates using the supravital stain neutral red. We describe a validation of the method and demonstrate its application to study the effects of hormones (i.e., parathyroid hormone) and cytokines (i.e., tumor necrosis factor-alpha) on the growth of primary cultures of adherent osteoblast-like cells. In addition we show that this method can also be applied to conveniently determine proliferation of cells which grow in suspension, like the CTLL-2 and B-9 cells, which are widely used to measure IL-2 and IL-6 bioactivity, respectively. In these bioassays the changes in optical density induced by IL-2 and IL-6 measured with the neutral red assay are directly comparable with the relative changes measured with the [3H]thymidine incorporation assay. For all types of cells tested, the optical density at 550 nm was directly proportional to the number of cells. The assay, which can be used for different purposes, is an excellent alternative to already existing methods. It is not only easy to perform but also very reproducible, making it ideal for screening of large numbers of samples. Therefore this assay offers a reliable and flexible tool to determine both stimulatory and inhibitory effects of hormones, cytokines, and drugs on cell growth or to study the effects on cell viability.

Cytotoxic effects of topical antimicrobial and antiseptic agents on human keratinocytes in vitro

The cytotoxicity of commonly used antimicrobial and antiseptic agents to cultured human keratinocytes was investigated, combining a morphologic assay with a quantitative neutral red (NR) spectrophotometric assay. Main outcome criteria of response were the initial cytotoxicity (NR 90) and midpoint cytotoxicity (NR 50) and the highest tolerated dose (HTD), a concentration causing the first observed morphologic alterations. These values were compared with commonly administered clinical doses or calculated doses. Thirty-five agents were evaluated; five agents were also subjected to an assay for cell morphologic alterations, and HTD and percentage of cells taking up trypan blue and annihilation dose were assessed. These studies show that in clinical concentrations many, but not all, agents exert profound cytotoxic effects. The results suggest that under certain conditions cultured epithelial grafts may be exposed to clinical concentrations of neomycin, clindamycin, framycetin, erythromycin, gentamicin, and 0.1% solutions of povidone-iodine. Tetrachlorodecaoxygen anion complex (TCDO) should be further evaluated as a likely effective cleansing agent before culture grafting.

Parathyroid hormone-related peptide as an endogenous inducer of parietal endoderm differentiation

Parathyroid hormone related peptide (PTHrP), first identified in tumors from patients with the syndrome of "Humoral Hypercalcemia of Malignancy," can replace parathyroid hormone (PTH) in activating the PTH-receptor in responsive cells. Although PTHrP expression is widespread in various adult and fetal tissues, its normal biological function is as yet unknown. We have examined the possible role of PTHrP and the PTH/PTHrP-receptor in early mouse embryo development. Using F9 embryonal carcinoma (EC) cells and ES-5 embryonic stem (ES) cells as in vitro models, we demonstrate that during the differentiation of these cells towards primitive and parietal endoderm-like phenotypes, PTH/PTHrP-receptor mRNA is induced. This phenomenon is correlated with the appearance of functional adenylate cyclase coupled PTH/PTHrP-receptors. These receptors are the mouse homologues of the recently cloned rat bone and opossum kidney PTH/PTHrP-receptors. Addition of exogenous PTH or PTHrP to RA-treated EC or ES cells is an efficient replacement for dBcAMP in inducing full parietal endoderm differentiation. Endogenous PTHrP is detectable at very low levels in undifferentiated EC and ES cells, and is upregulated in their primitive and parietal endoderm-like derivatives as assessed by immunofluorescence. Using confocal laser scanning microscopy on preimplantation mouse embryos, PTHrP is detected from the late morula stage onwards in developing trophectoderm cells, but not in inner cell mass cells. In blastocyst stages PTHrP is in addition found in the first endoderm derivatives of the inner cell mass. Together these results indicate that the PTH/PTHrP-receptor signalling system serves as a para- or autocrine mechanism for parietal endoderm differentiation in the early mouse embryo, thus constituting the earliest hormone receptor system involved in embryogenesis defined to date.

The effect of tissue type plasminogen activator (tPA) on osteoclastic resorption in embryonic mouse long bone explants: a possible role for the growth factor domain of tPA

Osteoblasts produce proteolytic enzymes and their production is regulated by osteotropic agents. It has been suggested that these proteases play a role in bone resorption by removing the superficial collagenous layer from the bone matrix and indirectly inducing migration of osteoclast precursors towards the bone matrix. We examined the effect of the plasminogen activator tPA on osteoclastic resorption using 17-day-old mouse embryonic long bone explants representing different stages of osteoclast development, that is, radii containing already mature osteoclasts and metacarpals containing no mature osteoclasts but only osteoclast precursors/progenitors which are still confined to the periosteum. Tissue type PA stimulated osteoclastic resorption (measured as 45Ca-release) in 17-day-old fetal metacarpals but not in radii of the same animal. Blocking the enzymatic activity of tPA did not inhibit its effect on osteoclastic resorption. Plasmin, the direct product of PA enzymatic activity, did not induce osteoclastic resorption. However, a tPA-mutant missing the growth-factor-like domain of the molecule, failed to stimulate 45Ca-release from the metacarpals. In addition, in both systems tPA and transforming growth factor alpha had similar effects on osteoclastic resorption. The finding that tPA stimulated 45Ca-release only in the metacarpals suggests that tPA has an effect on osteoclast formation rather than on the activity of already mature osteoclasts. Under the experimental conditions used this effect seems to be mediated by the growth factor domain of tPA rather than by the enzymatic activity of the molecule.

Osteoclast formation together with interleukin-6 production in mouse long bones is increased by insulin-like growth factor-I

Insulin-like growth factor-I (IGF-I) is a potent stimulator of bone formation. Whether this growth factor also induces bone resorption has not been studied in detail. We used two organ culture systems to examine the direct effect of IGF-I on bone resorption. Fetal mouse radii/ulnae, containing mature osteoclasts, showed no response to IGF-I, indicating that osteoclastic activity is not influenced by IGF-I. Fetal mouse metacarpals/metatarsals, containing just osteoclast precursors and progenitors, showed an increase in resorption in response to IGF-I, indicating that IGF-I stimulates the formulation of osteoclast precursors/progenitors and thereby increases the number of osteoclasts. Interleukin-6 (IL-6) has been hypothesized to be a mediator of bone resorptive agents such as parathyroid hormone (PTH). Both radii/ulnae and metacarpals/metatarsals reacted to IGF-I with an increase in IL-6 production. IL-6 production by UMR-106 osteogenic osteosarcoma cells was positively modulated by IGF-I, indicating that osteoblasts are likely to be the cells responsible for increased IL-6 production by the bones, and that IL-6 might be a mediatory of IGF-I-stimulated bone resorption.

Regulation of parathyroid hormonelike protein production in cultured normal and malignant keratinocytes

We have recently demonstrated that parathyroid hormone-like protein (PLP) production by cultured human squamous carcinoma cells (SCC) can be modulated by co-culture with fibroblasts. The interaction of SCC with fibroblasts, possibly occurring during the invasive phase of SCC, may be the stimulus for enhanced PLP production, thus contributing to the genesis of humoral hypercalcemia of malignancy in this type of cancer (Cancer Res 50:3589-3594, 1990). In the present study we show that the fibroblast-induced increase in PLP level in the medium of SCC-4 cells is paralleled by an increase in PLP messenger ribonucleic acid (mRNA) expression in these cells. We also found that the inhibition of secretion of PLP by monensin for 2 h resulted in a marked increase in immunodetectable PLP intracellularly, suggesting that secretion of PLP was a fast process. The modulation of the production of PLP by calcium and hydrocortisone was further examined in SCC-4 cells and was compared to that in normal keratinocytes and in SCC-9 cells. PLP levels in conditioned media were highest in poorly differentiating SCC-4 cells, intermediate in moderately differentiating SCC-9 cells, and lowest in normal keratinocytes showing high differentiating capacity. Furthermore, in each of the cell types used, PLP production was highest in cultures grown under low calcium conditions; at both calcium concentrations used, the presence of hydrocortisone reduced the PLP release into the medium. This reduction was probably due to a direct effect of hydrocortisone on PLP synthesis because the expression of PLP mRNA was also reduced in the presence of hydrocortisone when tested in SCC-4 cells. In conclusion, our findings indicate that the induction of differentiation in both normal and malignant keratinocytes is associated with the inhibition of PLP production.

Effect of macrophage colony-stimulating factor on in vitro osteoclast generation and bone resorption

To investigate the role of recombinant human macrophage colony-stimulating factor (rhM-CSF) on in vitro bone resorption, two bone explants, each at a different developmental stage, were adopted, namely 1) radii and 2) metatarsals of 17-day-old embryonic mice. At this stage of gestation, bone resorption in the radii is exclusively dependent upon fusion of osteoclast precursors and activation of mature osteoclasts, whereas in metatarsals it is dependent upon the generation of new osteoclasts. rhM-CSF showed no effect in radii, but stimulated 45Ca release in metatarsals, when they were either intact or periosteum stripped in coculture with embryonal liver as a source of hemopoietic progenitors. The rhM-CSF-induced increase in 45Ca release was paralleled by a higher number of osteoclasts. The stimulating effect was found to be in a concentration range between 250-500 U/ml M-CSF. The action of rhM-CSF was blocked by irradiation, indicating that it is dependent upon cell proliferation. These results, thus, show that M-CSF stimulates bone resorption only when it is dependent on generation of new osteoclasts. M-CSF does not appear to have any effect on the activity of mature osteoclasts. The mechanism of action might be direct on osteoclast precursors or indirect on accessory cells influencing osteoclast generation.

The use of bisphosphonates in the treatment of osteoporosis

The efficacy of bisphosphonates in the treatment of conditions characterized by increased osteoclastic bone resorption has been established. Recent evidence indicates that these compounds are also effective in the treatment of patients with osteoporosis. Two main protocols have been tried. One is based on the intermittent administration of the bisphosphonate, which is expected to decrease bone resorption, and give a drug-free period during which bone formation may proceed at a normal rate, leading to a positive calcium balance. The other argues that the resetting of the equilibrium in a cyclical process is, as a rule, incomplete and continuous low-grade suppression of resorption will result in a continuing positive bone balance. Intermittent administration of the first generation bisphosphonate, etidronate, for up to three years increases trabecular bone density, stabilizes it after two years, and appears to reduce the rate of new vertebral fractures in women with postmenopausal osteoporosis. Longer follow-up studies are needed before this beneficial effect is unequivocally established. Continuous administration of the second-generation bisphosphonate, pamidronate, increases spinal bone density in patients with osteoporosis linearly for up to four years, and is associated with a low rate of new vertebral fractures. These results need to be confirmed in controlled studies involving more patients. There are indications that pamidronate given continuously can prevent glucocorticoid-induced bone loss. There is no information about the effects of bisphosphonates on non-vertebral fractures. There are limited data about the use of bisphosphonates in the prevention of postmenopausal bone loss. Extensive studies on efficacy and safety are needed before this treatment is offered as an alternative to hormone replacement therapy.

Modulation of PTH-stimulated osteoclastic resorption by bisphosphonates in fetal mouse bone explants

We examined the effects of the bisphosphonates Cl2MDP, APD, and Me2APD on osteoclastic resorption in the absence and presence of PTH using fetal mouse osteoclast-free bone explants cocultured with fetal liver as a source of osteoclast precursors. Results revealed qualitative and quantitative differences among the bisphosphonates tested. With Cl2MDP and APD fractional inhibition of resorption (measured as 45Ca release) in the presence of PTH was proportional to that obtained in its absence. In contrast, Me2APD, which is the most potent inhibitor of the three, was found at low concentrations (less than or equal to 5 x 10(-7) M) to enhance the PTH-stimulated osteoclastic resorption. APD as well, at concentrations that could not inhibit resorption, had a similar effect, but Cl2MDP did not. These studies describe a new phenomenon, that low doses of nitrogen-containing bisphosphonates can act synergistically with PTH and enhance osteoclastic resorption. These findings may have clinical implications in the management of patients with increased osteoclastic resorption due to parathyroid overactivity.

Regulation of the production of plasminogen activators by bone resorption enhancing and inhibiting factors in three types of osteoblast-like cells

Production of proteolytic enzymes by osteoblasts is considered to be important for the initiation of osteoclastic bone resorption. We examined the production of tissue-type (tPA) and urokinase-type plasminogen activator (uPA) activity by three types of osteoblast-like cells (normal rat osteoblasts, rat and human osteosarcoma cells) using a quantitative spectrophotometric assay and a qualitative gel overlay technique. All 3 types of cells released both types of PA-activity into the medium, but normal rat osteoblasts released uPA probably in an inactive form. Treatment with different concentrations of the bone resorbing factors bovine Parathyroid Hormone [1-84], synthetic human Parathyroid Hormone-Like Protein [1-34]. Prostaglandin E2, Interleukin-1 beta, Tumor Necrosis Factor alpha and 1,25-dihydroxyvitamin D3 increased in general the production of both PA's by all three cell types. However, there were differences in the relative potencies of these factors. In contrast, Transforming Growth Factor beta, which inhibits bone resorption, decreased PA-activity in osteoblast-like cells. In all three types of cells, under control as well as under stimulated conditions, a high molecular weight form of PA was demonstrated by the gel overlay technique, most likely a complex of tPA with the PA-inhibitor PAI-1. The uniform increase in production of PA's by osteoblast-like cells in response to bone resorbing factors and its decrease by TGF beta supports the notion that PA's are involved in bone resorption. The exact mechanism however, remains to be elucidated.

A new competition binding assay for determination of the cAMP content of human leukocytes

We developed a competition binding assay for measurement of the cAMP content of human cells based on specific binding sites for this messenger in a crude bovine adrenocortical preparation. The mean cAMP content of human granulocytes and lymphocytes was 1.13 +/- 0.32 microM and 1.81 +/- 0.23 microM, respectively. Stimulation of granulocytes with formyl-methionyl-leucyl-phenylalanine (f-MLP) induced a 2-3 fold increase in cAMP between 10 and 45 sec, which returned to resting values after 1 min. Lymphocytes did not react to f-MLP with a transient rise in intracellular cAMP content. This competition binding assay for cAMP is in essence similar to that for Ins(1,4,5)P3 (7), but conditions for the simultaneous assessment of both messengers could not be found. The present assay is rapid, easy to perform, sensitive and considerably cheaper than commercial kits for assessment of the cAMP content of cells.

Modulation of the production of a parathyroid hormone-like protein in human squamous carcinoma cell lines by interaction with fibroblasts

Normal human keratinocytes as well as human squamous cell carcinomas produce a parathyroid hormone-like protein (PLP). However, PLP production by these cells is not a constant phenomenon. Since nothing is known about factors which regulate the production of PLP, in vitro studies were performed with normal keratinocytes and squamous carcinoma cell lines in order to establish conditions under which PLP production may vary. PLP was measured as cyclic AMP production in parathyroid hormone target cells (osteoblasts) which could be inhibited by a parathyroid hormone antagonist. The presence of PLP was confirmed using a radioimmunoassay specific for PLP. Results from the bioassay correlated very well with the data obtained by radioimmunoassay for PLP. The results confirm that human squamous carcinoma cells and normal keratinocytes produce PLP. PLP production appeared to be very sensitive to modulation of coculture of squamous carcinoma cells with fibroblasts. The effect of fibroblasts was not mediated by an effect on squamous carcinoma cell viability. Murine transformed fibroblasts (3T3 cells) as well as human normal foreskin fibroblasts were equally effective in inducing PLP production in these cells. The fibroblastic factor was apparently present in a soluble form in the coculture system which prevented direct cell-cell contact but allowed communication through the medium. Nevertheless, conditioned medium from 3T3 cells failed to induce PLP production by squamous carcinoma cells. This suggests a more complicated interaction between the two cell types than a one way message from fibroblasts to keratinocytes. Production of PLP by a number of squamous carcinoma cell lines was variable and not evidently correlated with the ability of these carcinoma cells to differentiate. Production of parathyroid hormone-like protein not only is the expression of a disturbed metabolism of a specific cell type but also reflects the cell-cell interaction in tumor tissue.

Application of an in vitro model and a clinical protocol in the assessment of the potency of a new bisphosphonate

The development of new bisphosphonates for clinical use requires congruence between the results of basic and clinical investigations. We have previously shown that this can be achieved with the use of an in vitro coculture mouse metacarpal resorption system sensitive to the activation of osteoclast precursors together with a clinical protocol in which the rate of decrease in urinary hydroxyproline excess with bisphosphonate treatment is assessed in patients with Paget's disease. In these studies bisphosphonates of known potencies were used. In the present study we have evaluated these approaches prospectively in the assessment of the antiresorptive potency of the new bisphosphonate (3-dimethylamino-1-hydroxypropylidene)-1,1-bisphosphonate (dimethyl-APD). A total of 42 patients with Paget's disease of bone received dimethyl-APD in doses predicted from the in vitro system. A total of 24 patients received the bisphosphonate intravenously (2, 4, and 8 mg/day) in groups of 8 patients each and 18 orally (100, 200, and 400 mg/day) in groups of 6 patients each for 10 days. Dimethyl-APD therapy was highly effective in inhibiting bone resorption. Urinary hydroxyproline excretion reached 30.9 +/- 5.6, 17.1 +/- 3.1, and 2.1 +/- 5.3% of initial excess after 10 days treatment with intravenous dimethyl-APD, 2, 4, and 8 mg/day, and 37.4 +/- 18, 10.4 +/- 8.5, and 13 +/- 4.1% with oral therapy, 100, 200, and 400 mg/day, respectively. Comparison of the antiresorptive potency of dimethyl-APD with that of APD showed that the former is roughly five times more potent, as predicted in the in vitro study.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone (PTH) and PTH-like protein (PLP) stimulate interleukin-6 production by osteogenic cells: a possible role of interleukin-6 in osteoclastogenesis

Osteogenic cells mediate PTH-stimulated osteoclastic bone resorption by a yet unidentified mechanism. We show that primairy rat osteoblast-like cells and the clonal osteogenic sarcoma cell line UMR-106 produce interleukin-6 (IL-6) and that bPTH(1-84) and synthetic hPLP(1-34) stimulate this production dose-dependently. With both peptides a close relation between IL-6 and cyclic-AMP production was found, though for PTH concentrations higher than 2.10(-8) M a clear dissociation was observed. Significant IL-6 activity was also detected in media of cultures of 17-day-old fetal mouse radii and metacarpals which was clearly stimulated by PTH. The source of IL-6 in these bone explants seems to be the osteogenic (cartilage) cells. Treatment of bone explants with IL-6 induced osteoclastic resorption which, however, depended on the bone resorption system used. This bone resorbing action of IL-6 is exerted probably through an effect on the formation of osteoclasts (osteoclastogenesis) rather than on the activation of already existing mature osteoclasts. We suggest that IL-6 produced by osteogenic cells may be a mediator in PTH-stimulated osteoclastic bone resorption.