Beneficial effects of manually assisted chiropractic adjusting instrument in a rabbit model of osteoarthritis

Osteoarthritis (OA) is a degenerative disease characterized by injury of all joint tissues. Our previous study showed that in experimental osteoporosis, chiropractic manipulation (CM) exerts protective effects on bone. We here assessed whether CM might ameliorate OA by improving subchondral bone sclerosis, cartilage integrity and synovitis. Male New-Zealand rabbits underwent knee surgery to induce OA by anterior cruciate ligament injury. CM was performed using the chiropractic instrument ActivatorV 3 times/week for 8 weeks as follows: force 2 setting was applied to the tibial tubercle of the rabbit right hind limb (TM-OA), whereas the corresponding left hind limb received a false manipulation (FM-OA) consisting of ActivatorV firing in the air and slightly touching the tibial tubercle. After sacrifice, subchondral bone integrity was assessed in the tibiae by microCT and histology. Cartilage damage and synovitis were estimated by Mankin's and Krenn's scores, respectively, and histological techniques. Bone mineral density and content in both cortical and trabecular compartments of subchondral bone decreased in OA rabbits compared to controls, but partially reversed in the TM-OA group. Trabecular bone parameters in the latter group also showed a significant improvement compared to FM-OA group. Moreover RANKL, OPG, ALP and TRAP protein expression in subchondral bone significantly decreased in TM-OA rabbits with respect to FM-OA group. CM was associated with lower Mankin's and Krenn's scores and macrophage infiltrate together with a decreased protein expression of pro-inflammatory, fibrotic and angiogenic factors, in TM-OA rabbits with respect to FM-OA. Our results suggest that CM may mitigate OA progression by improving subchondral bone as well as cartilage and synovial membrane status.

Osteostatin potentiates the bioactivity of mesoporous glass scaffolds containing Zn2+ ions in human mesenchymal stem cells

There is an urgent need of biosynthetic bone grafts with enhanced osteogenic capacity. In this study, we describe the design of hierarchical meso-macroporous 3D-scaffolds based on mesoporous bioactive glasses (MBGs), enriched with the peptide osteostatin and Zn2+ ions, and their osteogenic effect on human mesenchymal stem cells (hMSCs) as a preclinical strategy in bone regeneration. The MBG compositions investigated were 80%SiO2-15%CaO-5%P2O5 (in mol-%) Blank (BL), and two analogous glasses containing 4% ZnO (4ZN) and 5% ZnO (5ZN). By using additive fabrication techniques, scaffolds exhibiting hierarchical porosity: mesopores (around 4 nm), macropores (1-600 μm) and big channels (∼1000 μm), were prepared. These MBG scaffolds with or without osteostatin were evaluated in hMCSs cultures. Zinc promoted hMSCs colonization (both the surface and inside) of MBG scaffolds. Moreover, Zn2+ ions and osteostatin together, but not independently, in the scaffolds were found to induce the osteoblast differentiation genes runt related transcription factor-2 (RUNX2) and alkaline phosphatase (ALP) in hMSCs after 7 d of culture in the absence of an osteogenic differentiation-promoting medium. These results add credence to the combined use of zinc and osteostatin as an effective strategy for bone regeneration applications. STATEMENT OF SIGNIFICANCE: Mesoporous bioactive glasses (MBGs) are bioceramics whose unique properties make them excellent materials for bone tissue engineering. Physico-chemical characterization of MBGs as scaffolds made by rapid prototyping, doped with zinc (potential osteogenic, angiogenic and bactericidal ion) and loaded with osteostatin (osteogenic peptide) are described. These Zn-MBGs scaffolds showed 3D hierarchical meso-macroporous structure that enables to host and release osteostatin. When decorated with human mesenchymal stem cells (hMSCs), MBGs scaffoldsenriched with both zinc and osteostatin exhibited a synergistic effect to enhance hMSCs growth, and also hMSCs osteogenic differentiationwithout addition of other osteoblastic differentiation factors to the culture medium. This novel strategy has a great potential for use in bone tissue engineering.

Parathyroid hormone-related protein exhibits antioxidant features in osteoblastic cells through its N-terminal and osteostatin domains

Objectives

Oxidative stress plays a major role in the onset and progression of involutional osteoporosis. However, classical antioxidants fail to restore osteoblast function. Interestingly, the bone anabolism of parathyroid hormone (PTH) has been shown to be associated with its ability to counteract oxidative stress in osteoblasts. The PTH counterpart in bone, which is the PTH-related protein (PTHrP), displays osteogenic actions through both its N-terminal PTH-like region and the C-terminal domain.

Methods

We examined and compared the antioxidant capacity of PTHrP (1-37) with the C-terminal PTHrP domain comprising the 107-111 epitope (osteostatin) in both murine osteoblastic MC3T3-E1 cells and primary human osteoblastic cells.

Results

We showed that both N- and C-terminal PTHrP peptides at 100 nM decreased reactive oxygen species production and forkhead box protein O activation following hydrogen peroxide (H₂O₂)-induced oxidation, which was related to decreased lipid oxidative damage and caspase-3 activation in these cells. This was associated with their ability to restore the deleterious effects of H₂O₂ on cell growth and alkaline phosphatase activity, as well as on the expression of various osteoblast differentiation genes. The addition of Rp-cyclic 3′,5′-hydrogen phosphorothioate adenosine triethylammonium salt (a cyclic 3',5'-adenosine monophosphate antagonist) and calphostin C (a protein kinase C inhibitor), or a PTH type 1 receptor antagonist, abrogated the effects of N-terminal PTHrP, whereas protein phosphatase 1 (an Src kinase activity inhibitor), SU1498 (a vascular endothelial growth factor receptor 2 inhibitor), or an anti osteostatin antiserum, inhibited the effects of C-terminal PTHrP.

Conclusion

These findings indicate that the antioxidant properties of PTHrP act through its N- and C-terminal domains and provide novel insights into the osteogenic action of PTHrP.

Cite this article: S. Portal-Núñez, J. A. Ardura, D. Lozano, I. Martínez de Toda, M. De la Fuente, G. Herrero-Beaumont, R. Largo, P. Esbrit. Parathyroid hormone-related protein exhibits antioxidant features in osteoblastic cells through its N-terminal and osteostatin domains. Bone Joint Res 2018;7:58–68. DOI: 10.1302/2046-3758.71.BJR-2016-0242.R2.

Impact of Chiropractic Manipulation on Bone and Skeletal Muscle of Ovariectomized Rats

Evidence suggests that chiropractic manipulation might exert positive effects in osteoporotic patients. The aim of this study was to evaluate the effects of chiropractic manipulation on bone structure and skeletal muscle in rats with bone loss caused by ovariectomy (OVX). The 6-month old Sprague-Dawley rats at 10 weeks following OVX or sham operation (Sh) did not suffer chiropractic manipulation (NM group) or were submitted to true chiropractic manipulation using the chiropractic adjusting instrument Activator V^® three times/week for 6 weeks as follows: Force 1 setting was applied onto the tibial tubercle of the rat right hind limb (TM group), whereas the corresponding left hind limb received a false manipulation (FM group) consisting of ActivatorV^® firing in the air and slightly touching the tibial tubercle. Bone mineral density (BMD) and bone mineral content (BMC) were determined in long bones and L3-L4 vertebrae in all rats. Femora and tibia were analyzed by μCT. Mechano growth factor (MGF) was detected in long bones and soleus, quadriceps and tibial muscles by immunohistochemistry and Western blot. The decrease of BMD and BMC as well as trabecular bone impairment in the long bones of OVX rats vs Sh controls was partially reversed in the TM group versus FM or NM rats. This bone improvement by chiropractic manipulation was associated with an increased MGF expression in the quadriceps and the anterior tibial muscle in OVX rats. These findings support the notion that chiropractic manipulation can ameliorate osteoporotic bone at least partly by targeting skeletal muscle.

Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the "race for the surface" theory

Objectives

Implant-related infection is one of the most devastating complications in orthopaedic surgery. Many surface and/or material modifications have been developed in order to minimise this problem; however, most of the in vitro studies did not evaluate bacterial adhesion in the presence of eukaryotic cells, as stated by the ‘race for the surface’ theory. Moreover, the adherence of numerous clinical strains with different initial concentrations has not been studied.

Methods

We describe a method for the study of bacterial adherence in the presence of preosteoblastic cells. For this purpose we mixed different concentrations of bacterial cells from collection and clinical strains of staphylococci isolated from implant-related infections with preosteoblastic cells, and analysed the minimal concentration of bacteria able to colonise the surface of the material with image analysis.

Results

Our results show that clinical strains adhere to the material surface at lower concentrations than collection strains. A destructive effect of bacteria on preosteoblastic cells was also detected, especially with higher concentrations of bacteria.

Conclusions

The method described herein can be used to evaluate the effect of surface modifications on bacterial adherence more accurately than conventional monoculture studies. Clinical strains behave differently than collection strains with respect to bacterial adherence.

Cite this article: M. Martinez-Perez, C. Perez-Jorge, D. Lozano, S. Portal-Nuñez, R. Perez-Tanoira, A. Conde, M. A. Arenas, J. M. Hernandez-Lopez, J. J. de Damborenea, E. Gomez-Barrena, P. Esbrit, J. Esteban. Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the “race for the surface” theory. Bone Joint Res 2017;6:315–322. DOI: 10.1302/2046-3758.65.BJR-2016-0226.R2.

Functional roles of the nuclear localization signal of parathyroid hormone-related protein (PTHrP) in osteoblastic cells

PTHrP is an important regulator of bone remodelling, apparently by acting through several sequence domains. We here aimed to further delineate the functional roles of the nuclear localization signal (NLS) comprising the 88-107 amino acid sequence of PTHrP in osteoblasts. PTHrP mutants from a human PTHrP (-36/+139) cDNA (wild type) cloned into pcDNA3.1 plasmid with deletion (Δ) of the signal peptide (SP), NLS, T(107), or T107A replacing T(107) by A(107) were generated and stably transfected into osteoblastic MC3T3-E1 cells. In these cells, intracellular trafficking, cell proliferation and viability, as well as cell differentiation were evaluated. In these transfected cells, PTHrP was detected in the cytoplasm and also in the nucleus, except in the NLS mutant. Meanwhile, the PTH type 1 receptor (PTH1R) accumulates in the cytoplasm except for the ΔSP mutant in which the receptor remains at the cell membrane. PTHrP-wild type cells showed enhanced growth and viability, as well as an increased matrix mineralization, alkaline phosphatase activity, and osteocalcin gene expression; and these features were inhibited or abolished in ΔNLS or ΔT(107) mutants. Of note, these effects of PTHrP overexpression on cell growth and function were similarly decreased in the ΔSP mutant after PTH1R small interfering RNA transfection or by a PTH1R antagonist. The present in vitro findings suggest a mixed model for PTHrP actions on osteoblastic growth and function whereby this protein needs to be secreted and internalized via the PTH1R (autocrine/paracrine pathway) before NLS-dependent shuttling to the nucleus (intracrine pathway).

Characterization of Hybrid Bioactive Glass-polyvinyl Alcohol Scaffolds Containing a PTHrP-derived Pentapeptide as Implants for Tissue Engineering Applications

Hybrid foam (BG-PVA) with 50 % Bioactive glass (BG) and 50 % polyvinyl alcohol (PVA) was prepared by sol-gel process to produce scaffolds for bone tissue engineering. The pore structure of hydrated foams was evaluated by 3-D confocal microscopy, confirming 70% porosity and interconnected macroporous network. In this study, we assessed the putative advantage of coating with osteostatin pentapeptide into BG-PVA hybrid scaffolds to improve their bioactivity. In vitro cell culture experiments were performed using mouse pre-osteoblastic MC3T3-E1 cell line. The exposure to osteostatin loaded-BG-PVA scaffolds increase cell proliferation in contrast with the unloaded scaffolds. An in vivo study was selected to implant BG-PVA scaffolds, non-coated (Group A) or coated (Group B) with osteostatin into non critical bone defect at rabbit femur. Both groups showed new compact bone formation on implant surface, with lamellae disposed around a haversian canal forming osteons-like structure. We observed signs of inflammation around the implanted unloaded scaffold at one month, but resolved at 3 months. This early inflammation did not occur in Group B; supporting the notion that osteostatin may act as anti-inflammatory inhibitor. On the other hand, Group B showed increased bone formation, as depicted by many new trabeculae partly mineralized in the implant regenerating area, incipient at 1 month and more evident at 3 months after implantation. PVA/BG hybrid scaffolds present a porous structure suitable to support osteoblast proliferation and differentiation. Our in vitro and in vivo findings indicate that osteostatin coating improves the osteogenic features of these scaffolds.

Amylin exerts osteogenic actions with different efficacy depending on the diabetic status

Amylin displays osteogenic features, but its role in diabetic osteopenia is unclear. We examined the possible osteogenic action of amylin infusion for 3days into fructose-induced insulin-resistant (IR) and streptozotocin-induced type 2 diabetic (T2D) and normal (N) rats. Amylin failed to affect glycaemia or parathyroid hormone levels in any group, but reduced hyperinsulinemia in IR rats. In N rats, amylin increased bone formation rate and reduced osteoclast surface and erosive surface in the femoral metaphysis, and increased osteoprotegerin (OPG)/receptor activator of NFκB ligand (RANKL) mRNA ratio in the tibia. In T2D rats, amylin normalized trabecular structure parameters and increased osteoblast number and osteocalcin (OC) expression in long bones. In contrast, in IR rats, no apparent osteogenic effect of amylin in the femur was observed, although both OC and OPG/RANKL ratio were increased in the tibia. Our findings demonstrate a different osteogenic efficacy of amylin in two diabetic settings.

The C-terminal fragment of parathyroid hormone-related peptide promotes bone formation in diabetic mice with low-turnover osteopaenia

BACKGROUND AND PURPOSE

Current data suggest that parathyroid hormone (PTH)-related peptide (PTHrP) domains other than the N-terminal PTH-like domain contribute to its role as an endogenous bone anabolic factor. PTHrP-107-139 inhibits bone resorption, a fact which has precluded an unequivocal demonstration of its possible anabolic action in vivo. We thus sought to characterize the osteogenic effects of this peptide using a mouse model of diabetic low-turnover osteopaenia.

EXPERIMENTAL APPROACH

PTHrP-107-139 was administered to streptozotocin-induced diabetic mice, with or without bone marrow ablation, for 13 days. Osteopaenia was confirmed by dual-energy X-ray absorptiometry and microcomputed tomography analysis. Histological analysis was performed on paraffin-embedded bone tissue sections by haematoxylin/eosin and Masson's staining, and tartrate-resistent acid phosphatase immunohistochemistry. Mouse bone marrow stromal cells and osteoblastic MC3T3-E1 cells were cultured in normal and/or high glucose (HG) medium. Osteogenic and adipogenic markers were assessed by real-time PCR, and PTHrP and the PTH(1) receptor protein expression by Western blot analysis.

KEY RESULTS

PTHrP-107-139 reversed the alterations in bone structure and osteoblast function, and also promoted bone healing after marrow ablation without affecting the number of osteoclast-like cells in diabetic mice. This peptide also reversed the high-glucose-induced changes in osteogenic differentiation in both bone marrow stromal cells and the more differentiated MC3T3-E1 cells.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrate that PTHrP-107-139 promotes bone formation in diabetic mice. This mouse model and in vitro cell cultures allowed us to identify various anabolic effects of this peptide in this scenario.

Alterations of the Wnt/beta-catenin pathway and its target genes for the N- and C-terminal domains of parathyroid hormone-related protein in bone from diabetic mice

Type 1 diabetes mellitus (T1D) is associated with bone loss. Given that the Wnt/beta-catenin pathway is a major regulator of bone accrual, we assessed this pathway in mice with streptozotozin-induced T1D. In diabetic mouse long bones, we found alterations favouring the suppression of this pathway by using PCR arrays and beta-catenin immunostaining. Downregulation of sclerostin, an inhibitor of this pathway, also occurred, and related to increased osteocyte apoptosis. Our data show that both N- and C-terminal parathyroid hormone-related peptide fragments might exert osteogenic effects in this setting by targeting several genes of this pathway and increasing beta-catenin in osteoblastic cells.

Phytoestrogen modulation of bone-related cytokines and its impact on cell viability in human prostate cancer cells

AIMS

Prostate cancer (PCa) has a high propensity to metastasize to the bone. PCa cells produce several bone-related factors, namely parathyroid hormone related protein (PTHrP), its PTH type 1 receptor (PTH1R), osteoprotegerin (OPG), and receptor activator of NF-kappa B ligand (RANKL). The effects of these factors might explain, at least in part, the ability of PCa cells to grow in and interact with bone.

MAIN METHODS

We first analyzed the expression of the aforementioned factors (by western blot and flow cytometry), and their modulation by the phytoestrogens genistein and daidzein (as potential anti-tumoral agents), in human PCa cells in vitro. We also assessed the impact of these osteomimetic factors on PCa cell viability (by propidium iodide staining and flow cytometry, and trypan blue staining).

KEY FINDINGS

Genistein and daidzein, at nM range, increased both the PTHrP/PTH1R system and the OPG/RANKL protein ratio, while genistein and, to a lesser extent, daidzein, at >microM doses, inhibited cell viability in PCa cells. Both N- and C-terminal domains of PTHrP inhibited genistein-induced cell death by modulating transcription factor Runx-2 and the Bcl-2/Bax protein ratio in PCa cells.

SIGNIFICANCE

Our findings indicate that high doses of genistein and daidzein cause PCa cell death. On the other hand, low doses of these phytoestrogens induce some osteomimetic features in PCa cells with putative impact on PCa development.

Transient exposure to PTHrP (107-139) exerts anabolic effects through vascular endothelial growth factor receptor 2 in human osteoblastic cells in vitro

Intermittent administration of the N-terminal fragment of parathyroid hormone (PTH) and PTH-related protein (PTHrP) induces bone anabolic effects. However, the effects of the C-terminal domain of PTHrP on bone turnover remain controversial. We examined the putative mechanisms whereby this PTHrP domain can affect osteoblastic differentiation, using human osteosarcoma MG-63 cells and osteoblastic cells from human trabecular bone. Intermittent exposure to PTHrP (107-139), within 10-100 nM, for only <or=24 hours during cell growth stimulated alkaline phosphatase (ALP) and Runt homology domain protein (Runx2) activities as well as osteocalcin (OC) and osteoprotegerin (OPG) expression but inhibited receptor activator of nuclear factor kappaB (NF-kappaB) ligand. Continuous exposure to this PTHrP peptide reversed these effects. The stimulatory effects of transient treatment with PTHrP (107-139) on OC mRNA and/or OPG protein expression were unaffected by a neutralizing anti-insulin-like growth factor I antibody or [Asn(10), Leu(11), d-Trp(12)]PTHrP (7-34) in these cells. On the other hand, the former antibody and the latter PTHrP antagonist abrogated the PTHrP (1-36)-induced increase in these osteoblastic products. Transient exposure to PTHrP (107-139), in contrast to PTHrP (1-36), stimulated vascular endothelial growth factor receptor 2 (VEGFR2) mRNA levels in these cells. Moreover, induction of ALP activity as well as OC and OPG expression by PTHrP (107-139) was blunted by SU5614, a permeable tyrosine kinase inhibitor of VEGFR2. Protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) inhibitors abolished the PTHrP (107-139)-stimulated VEGFR2 and OPG mRNA levels in these cells. These results indicate that intermittent exposure to PTHrP (107-139) exerts potential anabolic effects through the PKC/ERK pathway and, subsequently, VEGFR2 upregulation in vitro in human osteoblastic cells.

The parathyroid hormone-related protein system and diabetic nephropathy outcome in streptozotocin-induced diabetes

The pathophysiology of the diabetic kidney (e.g., hypertrophy, increase urinary albumin excretion (UAE) is still ill-defined. Parathyroid hormone-related protein (PTHrP) is overexpressed in several nephropathies, but its role remains unclear. We evaluated the effect of high glucose on PTHrP and the PTH1 receptor (PTH1R) protein (by Western blot and immunohistochemistry) in the kidney of mice ith streptozotocin-induced diabetes, and in several mouse renal cells in vitro. Diabetic mice showed a significantly increased renal expression of PTHrP and PTH1R proteins with 2-8 weeks from the onset of diabetes. These animals exhibited an intense immunostaining for both proteins in the renal tubules and glomeruli. Using transgenic mice overexpressing PTHrP targeted to the renal proximal tubule, we found a significant increase in the renal hypertrophy index and in UAE in these diabetic mice relative to their control littermates. Moreover, logistic regression analysis showed a significant association between both PTHrP and PTH1R protein levels and UAE in all diabetic mice throughout the study. High-glucose (25 mm) medium was found to increase PTHrP and PTH1R in tubuloepithelial cells, mesangial cells and podocytes in vitro. Moreover, this increase in PTHrP (but not that of PTH1R) was inhibited by the AT1 receptor antagonist losartan. Collectively, these results indicate that the renal PTHrP/PTH1R system is upregulated in streptozotozin-induced diabetes in mice, and appears to adversely affect the outcome of diabetic renal disease. Our findings also suggest that angiotensin II might have a role in the PTHrP upregulation in this condition.

Sequential changes of parathyroid hormone related protein (PTHrP) in articular cartilage during progression of inflammatory and degenerative arthritis

OBJECTIVE

To investigate immunolocalisation of parathyroid hormone related protein (PTHrP) in two sequential models of experimental cartilage damage (inflammatory and degenerative) in order to elucidate differences in chondrocyte response to the disease.

METHODS

Immunohistochemistry with a polyclonal rabbit antiserum to the N-terminal domain of PTHrP was used to detect this protein in two different rabbit models sharing progressive cartilage damage: antigen induced arthritis (AIA) and osteoarthritis (OA) secondary to partial medial meniscectomy. Cartilage specimens from early (2 days in AIA; 8 weeks in experimental OA) and late (3 weeks in AIA; 52 weeks in OA) disease were compared.

RESULTS

Cell and matrix PTHrP staining in early AIA and OA was similar to that in controls. Late AIA cartilage showed a significant decrease in PTHrP positive cells and in the cartilage matrix. In contrast, at late OA stages, distinct PTHrP positivity was detected in proliferating cell clones, as assessed by proliferating cell nuclear antigen staining around cartilage damaged areas.

CONCLUSION

PTHrP staining of hyaline articular cartilage shows a different pattern during progression of each type of arthritis: an overall decrease associated with the inflammatory disease, and an increase in the proliferating chondrocyte clones with degenerative arthritis.

The interleukin-6/soluble interleukin-6 receptor system induces parathyroid hormone-related protein in human osteoblastic cells

In the present in vitro study, we tested the hypothesis that parathyroid hormone-related protein (PTHrP) might be a mediator of interleukin-6 (IL-6) and its soluble receptor (IL-6sR) in osteoblasts. We found that IL-6, within 1-20 ng/mL, added together with IL-6sR (100 ng/mL), rapidly (1 hour) increased PTHrP mRNA in human osteoblastic osteosarcoma MG-63 cells and human osteoblastic (hOB) cells from trabecular bone. PD098059, a mitogen-activated protein kinase (MAPK) kinase inhibitor, at 10 microM, and two inhibitors of protein prenylation and thus Ras activation, simvastatin (1 microM) and a farnesyltransferase (FTase) inhibitor (100 nM), but not the phosphatidylinositol 3-kinase inhibitor wortmannin, blocked the IL-6/IL-6sR-induced PTHrP expression in these cells. In addition, PD098059 as well as simvastatin and the FTase inhibitor abolished alkaline phosphatase activity and/or osteocalcin mRNA induction by the IL-6/IL-6sR in these cells. Our results support the role of the Ras/MAPK pathway as a major mechanism in the modulation of both PTHrP expression and differentiation in human osteoblasts.

Alendronate interacts with the inhibitory effect of 1,25(OH)2D3 on parathyroid hormone-related protein expression in human osteoblastic cells

The bisphosphonate alendronate is a potent inhibitor of bone resorption by its direct action on osteoclasts. In addition, there is some data suggesting that alendronate could also inhibit bone resorption indirectly by interacting with osteoblasts. Parathyroid hormone-related protein (PTHrP) produced by osteoblasts and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] are regulators of bone remodeling, which have interrelated actions in these cells. In this study, we assessed whether alendronate can affect PTHrP expression in the presence or absence of 1,25(OH)2D3 in human primary osteoblastic (hOB) cells from trabecular bone. Cell total RNA was isolated, and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was carried out using human PTHrP-specific primers. PTHrP in the hOB cell-conditioned medium was analyzed by a specific immunoradiometric assay. We found that PTHrP mRNA and secreted PTHrP were maximally inhibited by 10(-8) - 10(-6) M of 1,25(OH)2D3 treatment within 8-72 h in hOB cells. Alendronate (10(-14) - 10(-8) M) modified neither PTHrP mRNA nor PTHrP secretion, although it consistently abrogated the decrease in PTHrP production induced by 1,25(OH)2D3 in these cells. On the other hand, alendronate within the same dose range did not affect either the vitamin D receptor (VDR) mRNA or osteocalcin secretion, with or without 1,25(OH)2D3, in hOB cells. The inhibitory effect of alendronate on the 1,25(OH)2D3-induced decrease in PTHrP in these cells was mimicked by the calcium ionophore A23187 (5 x 10-6 M), while it was eliminated by 5 x 10(-5) M of nifedipine. Furthermore, although alendronate alone failed to affect [Ca2+]i in these cells, it stimulated [Ca2+]i after pretreatment of hOB cells with 10(-8) M of 1,25(OH)2D3, an effect that was abolished by 5 x 10(-5) M of nifedipine. These results show that alendronate disrupts the modulatory effect of 1,25(OH)2D3 on PTHrP production in hOB cells. Our findings indicate that an increase in calcium influx appears to be involved in the mechanism mediating this effect of alendronate.

Age-related changes in parathyroid hormone-related protein and vascular endothelial growth factor in human osteoblastic cells

Osteogenesis and angiogenesis occur in a coordinated manner in skeletal tissue, so that impaired angiogenesis is associated with decreased bone formation in aged subjects. However, the interaction between bone endothelium and osteoblastic cells is poorly understood. Parathyroid hormone-related protein (PTHrP), a bone factor which modulates osteoblastic cell growth and/or differentiation, stimulates vascular endothelial growth factor (VEGF), a potent angiogenic factor, in primary cultures of human osteoblastic (hOB) cells. In the present study, we examined the age-related changes of both factors in these cells. Human OB cells were isolated from trabecular bone samples from knee or hip explants obtained from 45 osteoarthritic patients: 12 <60 years (21-59 years), 5 women and 7 men, and 33 >60 years (61-82 years), 20 women and 13 men. Cell total RNA was isolated, and mRNA analysis was performed by reverse transcription-polymerase chain reaction. Relative ratios of amplified products with respect to glyceraldehyde-3-phosphate dehydrogenase were then calculated. PTHrP and VEGF were measured in the cell-conditioned medium, after stimulation with (or without) 10 nM 1,25(OH)(2)D(3) for 72 h, using specific immunoradiometric assay and a competitive immunoassay, respectively. A positive correlation was found between PTHrP and VEGF (both mRNA and secreted protein), and also between PTHrP mRNA and the secreted protein levels, in these cells. PTHrP, both mRNA and protein secretion levels, and VEGF secreted values were higher in knee hOB cells than in hip hOB cells only in the younger group. In addition, a decrease in the secreted levels of these factors occurs with aging only in hOB cells from knee. Treatment with 10 nM 1,25(OH)(2)D(3) induced a lower inhibitory response of PTHrP secretion, and a higher stimulatory response of secreted VEGF, in hOB cells with age. These findings indicate that age-related bone loss in humans is associated with a decrease in the osteoblastic secretion of both PTHrP and VEGF in the knee, a predominantly trabecular bone. These data might provide a rationale to explain the impaired angiogenesis associated with trabecular bone loss in aging.

Treatment of malignant hypercalcaemia

Hypercalcaemia is a common paraneoplastic syndrome caused by the production by tumours of several factors which affect bone resorption and/or tubular calcium reabsorption. Antihypercalcaemic therapy in cancer patients involves rehydration manoeuvres, as well as the use of a variety of available drugs which inhibit bone resorption, namely plicamycin, calcitonin, bisphosphonates and gallium nitrate. While plicamycin is currently out of use because of its considerable toxicity, bisphosphonates have become the standard therapy in hypercalcaemia of malignancy (HM). These compounds are potent inhibitors of bone resorption but they do not affect tubular calcium reabsorption, which limits their efficacy in humoral HM (HHM) cases. In these patients, gallium nitrate should be the therapy of choice. Among the available bisphosphonates, pamidronate administered in a single infusion of 90 mg, normalises serum calcium levels in > 90% of HM patients. A recently introduced bisphosphonate, zoledronate, is likely to replace pamidronate as a first-line therapy in these patients. The effectiveness of calcitonin in HM treatment is limited, although it seems to be useful at the outset in cases with severe symptomatic hypercalcaemia. Future treatment options of HM are likely to include new bone resorption inhibitors, for example, naturally-occurring osteoprotegerin, or alternate approaches aimed at reducing the tumour production of parathyroid hormone-related protein with noncalcaemic analogues of calcitriol or ras-isoprenylation inhibitors. The development of putative therapeutic agents targeted to inhibit distal calcium reabsorption should be valuable in the management of HHM cases.

Up-regulation of parathyroid hormone-related protein in folic acid-induced acute renal failure

BACKGROUND

Parathyroid hormone (PTH)-related protein (PTHrP) is present in many normal tissues, including the kidney. Current evidence supports that PTHrP is involved in renal pathophysiology, although its role on the mechanisms of renal damage and/or repair is unclear. Our present study examined the changes in PTHrP and the PTH/PTHrP receptor (type 1) in folic acid-induced acute renal failure in rats. The possible role of PTHrP on the process of renal regeneration following folic acid administration, and potential interaction between angiotensin II (Ang II) and endothelin-1, and PTHrP, were examined in this animal model.

METHODS

PTHrP, PTH/PTHrP receptor, ACE, and preproendothelin-1 (preproET-1) mRNA levels in the rat kidney were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and/or RNase protection assay. Immunohistochemistry also was performed for PTHrP, the PTH/PTHrP receptor, and Ang II in the renal tissue of folic acid-injected rats. The role of PTHrP on tubular cell proliferation following folic acid injury was investigated in vitro in rat renal epithelial cells (NRK 52E). PTHrP secretion in the medium conditioned by these cells was measured by an immunoradiometric assay specific for the 1-36 sequence.

RESULTS

Using RT-PCR, PTHrP mRNA was rapidly (1 hour) and maximally increased (3-fold) in the rat kidney after folic acid, decreasing after six hours. At 72 hours, renal function was maximally decreased in these rats, associated with an increased PTHrP immunostaining in both renal tubules and glomeruli. In contrast, the PTH/PTHrP receptor mRNA (RNase protection assay) decreased shortly after folic acid administration. Moreover, PTH/PTHrP receptor immunostaining dramatically decreased in renal tubular cell membranes after folic acid. A single subcutaneous administration of PTHrP (1-36), 3 or 50 microg/kg body weight, shortly after folic acid injection increased the number of tubular cells staining for proliferating cell nuclear antigen by 30% (P < 0.05) or 50% (P < 0.01), respectively, in these rats at 24 hours, without significant changes in either renal function or calcemia. On the other hand, this peptide failed to modify the increase (2-fold over control) in ACE mRNA, associated with a prominent Ang II staining into tubular cell nuclei, in the kidney of folic acid-treated rats at this time period. The addition of 10 mmol/L folic acid to NRK 52E cells caused a twofold increase in PTHrP mRNA at six hours, without significant changes in the PTH/PTHrP receptor mRNA. The presence of two anti-PTHrP antibodies, with or without folic acid, in the cell-conditioned medium decreased (40%, P < 0.01) cell growth.

CONCLUSIONS

Renal PTHrP was rapidly and transiently increased in rats with folic acid-induced acute renal failure, featuring as an early response gene. In addition, changes in ACE and Ang II expression were also found in these animals. PTHrP induces a mitogenic response in folic acid-damaged renal tubular cells both in vivo and in vitro. Our results support the notion that PTHrP up-regulation participates in the regenerative process in this model of acute renal failure and is a common event associated with the mechanisms of renal injury and repair.

C-terminal parathyroid hormone-related protein (PTHrP) (107-139) stimulates intracellular Ca(2+) through a receptor different from the type 1 PTH/PTHrP receptor in osteoblastic osteosarcoma UMR 106 cells

Studies were undertaken to determine whether PTH-related protein (PTHrP) (107-139) mobilizes [Ca(2+)](i) in osteoblastic osteosarcoma UMR 106 cells. PTHrP (107-139), in a manner similar to PTHrP (107-111), induced a rapid [Ca(2+)](i) response in these cells that was dose dependent (EC(50) of approximately 0.1 pM) and more efficient than that of PTHrP (1-36) (EC(50) of approximately 1 nM). This effect of PTHrP (107-139) was abrogated by micromolar doses of verapamil or nifedipine. However, it was unaffected by 10 microM U73122 (a phospholipase C inhibitor), 100 microg/ml heparin (an inositol 1,4,5-trisphosphate receptor inhibitor), or 400 ng/ml pertussis toxin (a G(i) inhibitor), which inhibited the [Ca(2+)](i) response to PTHrP (1-36), or by either 25 nM bisindolylmaleimide I (BIM), a protein kinase (PK) C inhibitor, or 1 microM phorbol-12-myristate-13-acetate preincubation (22 h). PTHrP (107-139) and PTHrP (1-36), at 100 nM, desensitized the [Ca(2+)](i) response to a second challenge with the same peptide, but not with the other peptide in these cells. PTHrP (7-34), a type 1 PTH/PTHrP receptor (PTH1R) antagonist, decreased the effect of PTHrP (1-36) on [Ca(2+)](i). In contrast, PTHrP (107-111), but neither PTHrP (109-138) nor PTHrP (7-34), abolished this effect of PTHrP (107-139). Both PTHrP (107-139) and PTHrP (1-36), added together at submaximal doses, induced a higher [Ca(2+)](i) response. Moreover, PTHrP (107-139) increased the efficacy of PTHrP (1-36) on [Ca(2+)](i), but decreased its induced increase in PKA activity in these cells. Verapamil or nifedipine (at 50 microM) or 25 nM BIM, but not 25 microM adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, a PKA inhibitor, abolished the PTHrP (107-139)-induced increase in interleukin 6 messenger RNA (assessed by RT, followed by PCR) in UMR 106 cells. This peptide also increased c-fos messenger RNA in these cells; an effect inhibited by BIM, but unaffected by either verapamil or EGTA. These findings support the existence of high-affinity receptors for PTHrP (107-139), associated with an induced Ca(2+) influx, different from the PTH1R in UMR 106 cells. The present results suggest that PTHrP could affect bone turnover by interacting with the PTH1R and other yet unknown receptors in bone cells through complex mechanisms.

Changes in osteocalcin response to 1,25-dihydroxyvitamin D(3) stimulation and basal vitamin D receptor expression in human osteoblastic cells according to donor age and skeletal origin

Age-related osteopenia is known to occur differently throughout the skeleton. In the present study, we examine the influence of donor age (<50 and >50 years), and bone structure (cortical vs. trabecular) on osteocalcin and vitamin D receptor (VDR) expression in primary cultures of human osteoblastic cells (hOB) cells. Cells were isolated from trabecular bone samples obtained from donors undergoing either knee (mainly trabecular) (n = 22; 4 <50 years, 18 >50 years) or hip (mainly cortical) (n = 16; 6 <50 years, 10 >50 years) arthroplasty. Pooling the results from knee and hip hOB cell cultures, we found that secreted osteocalcin was higher in hOB cells from the younger donors, compared with that in older donors, and peaked after stimulation with 10(-6)--10(-8) mol/L 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. In cells from the latter donors, this secretion was maximal after 10(-6) mol/L 1,25(OH)(2)D(3) treatment. On the other hand, using reverse transcription followed by polymerase chain reaction, baseline osteocalcin mRNA was found to be lower in hOB cells from the older donors than in those from younger donors. After treatment with 10(-6)--10(-8) mol/L 1,25(OH)(2)D(3), osteocalcin mRNA increased over baseline in all groups of hOB cells studied. In age-matched cultures, both basal and 10(-6)--10(-8) mol/L 1,25(OH)(2)D(3)-stimulated osteocalcin mRNA showed similar values in hOB cells from both skeletal sites in younger donors. However, in the older donors, baseline as well as 10(-8) mol/L 1,25(OH)(2)D(3)-stimulated osteocalcin mRNA were higher in knee hOB cells than in hip hOB cells. Furthermore, baseline VDR mRNA expression was also higher in the former cells than in the latter cells in the older group. Considering the influence of donor age at each skeletal site of origin, we found lower baseline osteocalcin and VDR mRNA levels in hip hOB cells in the older group than in the younger group. Our findings indicate that the response of osteocalcin secretion and its mRNA to physiological doses of 1,25(OH)(2)D(3) decreases with aging and is associated with decreased VDR mRNA expression in hOB cells from mainly cortical bone.

Parathyroid hormone-related protein as a renal regulating factor. From vessels to glomeruli and tubular epithelium

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) produce similar biological effects through the PTH/PTHrP receptor. Less is known about the physiological role of PTHrP, which was first identified as the agent of the humoral hypercalcemia of malignancy. Despite the widespread production of PTHrP in healthy individuals, the concentration of the protein is below the detectable limit of current assays, suggesting that PTHrP normally functions locally in an autocrine or paracrine manner. Thus, some differences in their biological activities have been described and they may be related to the presence of different receptors. In this regard, a second receptor that binds selectively to PTH has also been found. Recent studies have demonstrated the expression of both PTH/PTHrP receptor and protein in the renal glomeruli. Moreover, there are convincing data that support a direct role of PTH and PTHrP in modulating renal blood flow and glomerular filtration rate. This multifunctional protein, PTHrP, also has a proliferative effect on both glomerular mesangial cells and tubular epithelial cells. Increases in the expression of PTHrP have been observed in several experimental models of nephropathies, suggesting that PTHrP upregulation is a common event associated with the mechanism of renal injury and repair.

Hypercalcemia of malignancy--new insights into an old syndrome

Hypercalcemia is a common paraneoplastic syndrome. Tumors induce hypercalcemia by a local mechanism associated with the tumor's production of various cytokines increasing bone osteolysis. In addition, many tumors release humoral factors, mainly parathyroid hormone (PTH)-related protein (PTHrP), which stimulates bone resorption and/or tubular calcium reabsorption leading to hypercalcemia. Interaction of PTHrP with other tumor-elaborated cytokines might explain some nonPTH-like features associated with the hypercalcemia of malignancy syndrome. Using assays recognizing various PTHrP epitopes, the majority of hypercalcemic cancer patients have higher immunoreactive PTHrP levels in either plasma or urine than normal subjects. Present data support the concept that PTHrP might also be a factor which promotes tumor growth and also the development of osteolytic metastasis. A variety of therapeutic approaches are available to lower serum calcium in hypercalcemic cancer patients. The pathophysiological mechanisms of hypercalcemia appear to be a determinant of the efficacy of different antihypercalcemic treatments.

Cultures of human osteoblastic cells from dialysis patients: influence of bone turnover rate on in vitro selection of interleukin-6 and osteoblastic cell makers

The factors contributing to renal osteodystrophy are still incompletely characterized. A variety of cytokines and growth factors appear to have ill-defined roles in this disease. Our aim is to compare osteoblastic cell growth and different osteoblastic markers in vitro with histomorphometric bone parameters and some serum bone-turnover markers in vivo in dialysis patients with either high- (HTBD) or low-turnover (LTBD) bone disease. Six patients were diagnosed to have LTBD, and another five patients, HTBD. Intact parathyroid hormone (PTH) and osteocalcin (OC) levels in serum were greater in patients with HTBD than in those with LTBD. Osteoblastic cells isolated from iliac crest biopsy specimens were grown in culture medium for different times up to 13 days. Osteoblastic cell growth (cell number and area under the cell growth curve) was greater in patients with HTBD than in those with LTBD. Static and dynamic bone formation parameters correlated with serum PTH levels. No correlation was found between PTH and osteoblastic cell proliferation. OC, C-terminal type I procollagen, and alkaline phosphatase osteoblastic secretion in vitro were similar in the HTBD and LTBD groups. However, interleukin-6 (IL-6) secretion was greater in cells isolated from patients with LTBD. Our results indicate that osteoblastic cell growth and osteoblastic IL-6 secretion are related to bone turnover in patients with osteodystrophy. Our findings support the hypothesis that factors other than PTH level might have an important role in affecting osteoblastic function in renal osteodystrophy.

Relationship of plasma bone cytokines with hypercalcemia in cancer patients

The pathogenesis of cancer-associated hypercalcemia is not yet completely understood. This syndrome appears to be a consequence of the tumor production of humoral factors, mainly parathyroid hormone related protein (PTHrP). However, patients with humoral hypercalcemia of malignancy have features suggesting that factors other than PTHrP might play a role in this syndrome. We performed a case-control study in cancer patients with and without hypercalcemia. A total of 105 patients with a variety of tumors, 60 of them with hypercalcemia (corrected serum calcium over 2.6 mmol/l), and 45 without hypercalcemia. In a previous study, we demonstrated that plasma PTHrP was highly associated with hypercalcemia in these patients. In the present study, we measured the plasma levels of various bone cytokines: interleukin-1beta (IL-1beta), interleukin-6 (IL-6), transforming growth factor (TGF) alpha, and tumor necrosis factor (TNF) alpha, in these cancer patients. We also determined C-terminal type I procollagen (PICP) and C-terminal telopeptide of type I collagen (ICTP), bone formation and bone resorption markers, respectively, in serum in these patients. We found that these osteolytic cytokines do not increase in plasma by the presence of hypercalcemia. In fact, using a logistic regression analysis, a significant (P<0.02) association was found between the low plasma levels of IL-1beta and TGFalpha and hypercalcemia, independent of plasma PTHrP and the presence of bone metastasis, in these patients. No significant association between the plasma levels of IL-6 or TNFalpha and hypercalcemia was found in these cancer patients. Serum ICTP correlated (r=0.35; P=0.008) with hypercalcemia in these patients, but none of the cytokines studied in plasma correlated with either ICTP or PICP in these hypercalcemic patients. Our data indicate that the circulating levels of several bone cytokines are not enhanced by PTHrP in hypercalcemic cancer patients. The mechanism responsible for the association between the low plasma levels of some of these cytokines and hypercalcemia in these patients remains obscure. However, this finding does not rule out the possible local bone effects of these cytokines, contributing to hypercalcemia in cancer patients.

Characterization of parathyroid hormone/parathyroid hormone-related protein receptor and signaling in hypercalcemic Walker 256 tumor cells

Parathyroid hormone (PTH)-related protein (PTHrP) is the main factor responsible for humoral hypercalcemia of malignancy. Both PTH and PTHrP bind to the common type I PTH/PTHrP receptor (PTHR), thereby activating phospholipase C and adenylate cyclase through various G proteins, in bone and renal cells. However, various normal and transformed cell types, including hypercalcemic Walker 256 (W256) tumor cells, do not produce cAMP after PTHrP stimulation. We characterized the PTHrP receptor and the signaling mechanism upon its activation in the latter cells. Scatchard analysis of PTHrP-binding data in W256 tumor cells revealed the presence of high affinity binding sites with an apparent K(d) of 17 nM, and a density of 90 000 sites/cell. In addition, W256 tumor cells immunostained with an anti-PTHR antibody, recognizing its extracellular domain. Furthermore, reverse transcription followed by PCR, using primers amplifying two different regions in the PTHR cDNA corresponding to the N- and C-terminal domains, yielded products from W256 tumor cell RNA which were identical to the corresponding products obtained from rat kidney RNA. Consistent with our previous findings on cAMP production, 1 microM PTHrP(1-34), in contrast to 10 microg/ml cholera toxin or 1 microM isoproterenol, failed to affect protein kinase A activity in W256 tumor cells. However, in these cells we found a functional PTHR coupling to G(alpha)(q/11), whose presence was demonstrated in these tumor cell membranes by Western blot analysis. Our findings indicate that W256 tumor cells express the PTHR, which seems to be coupled to G(alpha)(q/11). Taken together with previous data, these results support the hypothesis that a switch from the cAMP pathway to the phospholipase C-intracellular calcium pathway, associated with PTHR activation, occurs in malignant cells.

Parathyroid hormone-related protein, parathyroid hormone, and vitamin D in hypercalcemia of malignancy

The pathogenesis of cancer-associated hypercalcemia is not yet completely understood. In the majority of cancer patients, hypercalcemia appears to be a consequence of the tumor production of parathyroid hormone (PTH)-related protein (PTHrP). However, patients with humoral hypercalcemia of malignancy, in contrast to those with primary hyperparathyroidism, have an uncoupled bone turnover, and they usually have low circulating levels of 1.25(OH)2D3. We performed a case-control study to assess the relationship of plasma PTHrP, PTH and 1.25(OH)2D3 with hypercalcemia in cancer patients with a variety of tumors. Sixty of these patients had hypercalcemia, and 45 were normocalcemic. We measured PTHrP and PTH by immunoradiometric assay (Nichols), and 1.25(OH)2D3 by radioreceptor assay (Nichols), in plasma in both groups of cancer patients. Using a logistic regression analysis, we found that the higher PTHrP in plasma, the higher association with hypercalcemia occurred in these patients. In addition, the decreased plasma levels of PTH and 1.25(OH)2D3 in the majority of cancer patients were found to be significantly associated with hypercalcemia. Our results indicate that the combined determination of PTH, PTHrP and 1.25(OH)2D3 in plasma represents a more comprehensive approach to the investigation of hypercalcemia in cancer patients. Our data also support the role of PTHrP as a humoral factor responsible for hypercalcemia in these patients.

Parathyroid hormone-related peptide stimulates DNA synthesis and insulin secretion in pancreatic islets

Parathyroid hormone (PTH)-related protein (PTHrP) is present in the pancreatic islet. Recent data in transgenic mice suggest that PTHrP might modulate islet mass and insulin secretion. In the present study, we assessed the effect of the N-terminal PTH-like region of PTHrP on DNA synthesis in isolated rat islets. PTHrP (1-34), between 1 pM and 10 nM, for 48 h stimulated []thymidine incorporation into rat islets. This effect was maximally induced, about 2.5-fold over control, by 10 pM of this peptide, decreasing thereafter. In contrast, PTHrP (38-64) amide or PTHrP (107-139) were ineffective in increasing DNA synthesis in islets. Using reverse transcription followed by PCR, we confirmed that rat islets express PTHrP and the type I PTH/PTHrP receptor. Addition of a neutralizing anti-PTHrP antibody to the incubation medium of proliferating islets decreased islet DNA synthesis by 30%. The effect of a submaximal dose (30 pM) of PTHrP (1-34) on DNA synthesis in rat islets was abolished by 25 nM bisindolylmaleimide I, a protein kinase C (PKC) inhibitor, but not by 25 microM adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, a protein kinase A inhibitor. Moreover, 100 nM phorbol-12-myristate-13-acetate for 48 h also increased DNA synthesis 2-fold over controls in islets. PTHrP (1-34), at 100 nM, in contrast to 50 microM forskolin or 10 mM NaF, failed to affect adenylate cyclase activity in islet membranes. PTHrP, at 30 pM, was also found to increase 2-fold insulin released into the islet-conditioned medium within 24-48 h. Our results suggest that PTHrP is a modulator of pancreatic islet growth and/or function by a PKC-mediated mechanism.

Effects of transforming growth factor beta1 on cell growth and parathyroid hormone-related protein in Walker 256 tumor cells

Hypercalcemic strains of the rat Walker 256 (W256) tumor synthesize parathyroid hormone-related protein (PTHrP) and at least one of them produces an ill-defined transforming growth factor activity. We tested the production of transforming growth factor (TGF) beta by a hypercalcemic W256 tumor strain, and assessed its effects on tumor cell growth and PTHrP expression. We found that addition of TGF beta1 for 7 days inhibited cell growth ([3H]thymidine incorporation and cell number) dose dependently, between 0.04-20 pM. The antiproliferative effect of TGF beta1 on W256 tumor cell growth was likely mediated by binding to high affinity receptors (Kd = 14 pM) in these cells. At different tumor cell growth stages, acidified cell-conditioned medium contained immunoreactive TGF beta1. However, the nonacidified tumor cell-conditioned medium was found to contain neither immunoreactive nor bioactive TGF beta. Moreover, exposure of W256 tumor cells to a neutralizing anti-TGF beta1 antibody failed to affect tumor cell proliferation. Thus, W256 tumor cells appear to secrete TGF beta in an inactive form. Using reverse transcription followed by PCR, we found that addition of 20 pM TGF beta1 increased its own mRNA expression, apparently by stimulating gene transcription, within 6-12 h in W256 tumor cells. In addition, 20 pM TGF beta1 stimulated PTHrP mRNA in these cells at 24 h; an effect which was mediated, at least in part, by increasing PTHrP mRNA stability. Immunoreactive PTHrP decreased in the W256 tumor cell-conditioned medium after treatment with 20 pM TGF beta1 for 24-48 h. These results support the validity of this W256 tumor strain for in vivo studies to clarify the relative role of TGF beta and PTHrP in the pathogenesis of humoral hypercalcemia of malignancy.

Parathyroid hormone-related protein (107-139) decreases alkaline phosphatase in osteoblastic osteosarcoma cells UMR 106 by a protein kinase C-dependent pathway

The C-terminal (107-111) region of parathyroid hormone-related protein (PTHrP) appears to inhibit osteoclastic bone resorption, and to affect osteoblastic growth and differentiation. We tested the effect of human PTHrP (107-139) on alkaline phosphatase (ALP) activity in osteoblastic osteosarcoma UMR 106 cells. We found that this C-terminal PTHrP peptide, between 10 nM and 10 fM, inhibited ALP activity in these cells during the log phase of growth. Human PTHrP (1-34) amide and human PTHrP (1-141) were as potent as PTHrP (107-139) in growing UMR 106 cells. This inhibitory effect of 10 nM PTHrP (107-139) on ALP activity was also observed in serum-depleted cells, and in the presence of 10 nM dexamethasone, which increased ALP activity by 40% in these cells. In addition, this effect of PTHrP (107-139) was blunted by 25 nM bisindolylmaleimide I, a protein kinase C inhibitor. These results support a role for the C-terminal region of PTHrP as a modulator of bone formation.

Parathyroid hormone-related protein (107-139) stimulates interleukin-6 expression in human osteoblastic cells

The N-terminal region of both parathyroid hormone (PTH) and PTH-related protein (PTHrP) binds to the same PTH/PTHrP receptor in osteoblasts. However, C-terminal PTHrP (107-139) inhibits growth and various functions of osteoblasts and osteoclasts apparently through PTHrP-specific receptors. PTH (1-34) and PTHrP (1-34) rapidly induce interleukin-6 (IL-6) expression by osteoblasts. The aim of the present study was to assess the effects of PTHrP (107-139) on IL-6 gene expression and secretion by osteoblastic cells from human trabecular bone (hOB). Using reverse transcription followed by PCR, it was found that IL-6 mRNA was twofold maximally increased by either PTHrP (1-34) or PTHrP (107-139), at 10 nM, over basal within 1 to 2 h in hOB cells. This effect of PTHrP (107-139), and that of PTHrP (1-34), were abolished by the transcription inhibitor actinomycin D. Meanwhile, puromycin, a protein synthesis inhibitor, superinduced IL-6 expression in the presence or absence of each PTHrP peptide. Both PTHrP (1-34) and PTHrP (107-139), but not PTHrP (38-64), stimulated IL-6 secretion to the hOB cell-conditioned medium at 24 h, dose dependently. In addition, this maximal stimulatory effect (twofold over basal) was similar with each PTHrP peptide alone, and not additive when added together. PTHrP (107-139) stimulation of mRNA and protein in hOB cells was abolished by bisindolylmaleimide I, a protein kinase C inhibitor, but not by either adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS), or N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89), two protein kinase A inhibitors. These results indicate that C-terminal PTHrP, like its N-terminal domain, induces IL-6 production by human osteoblastic cells. This effect of both PTHrP regions could provide a mechanism to modulate bone turnover.

Influence of skeletal site of origin and donor age on osteoblastic cell growth and differentiation

Bone loss with aging may be due, at least in part, to inadequate bone formation. Moreover, the process of bone aging is known to follow a different pattern throughout the skeleton. In this study, we examined the cell proliferation rate (area under the cell growth curve, AUC) and the secretion of C-terminal type I procollagen (PICP), alkaline phosphatase (ALP), and osteocalcin (OC) in primary cultures of osteoblastic cells from human trabecular bone. Osteoblastic cells were obtained for 168 donors (100 women and 68 men). Ninety-eight bone samples were obtained from subjects undergoing knee arthroplastia, 52 aged 50-70 years (64 +/- 5) and 46 over age 70 (73 +/- 2). Another 70 bone samples were obtained from subjects undergoing hip arthroplastia; 51 were 50-70 years old (64 +/- 4) and 19 were over 70 (75 +/- 5). Osteoblastic cells from the older donors had a lower proliferation rate and OC secretion than those from younger subjects. However, ALP secretion was higher in the former subjects, whereas PICP secretion was unchanged. Osteoblastic cells from hip had a lower proliferation rate than those from knee. PICP secretion was also lower and ALP secretion was higher in the former cells. In age-matched cell cultures, osteoblastic cells from the knee had higher proliferation rate and PICP secretion than osteoblastic cells from the hip. However, ALP secretion was lower in knee osteoblastic cells than those from hip only in the younger group. With aging, ALP secretion was found to increase in knee osteoblactic cells, whereas OC secretion decreased in osteoblastic cell cultures from the hip. Our findings suggest that bone loss with aging may be accounted for, at least in part, by a decreased osteoblastic cell proliferation and an increased osteoblastic maturation. In addition, our data indicate that these changes with aging do not occur similarly at different skeletal sites.

Influence of skeletal site of origin and donor age on 1,25(OH)2D3-induced response of various osteoblastic markers in human osteoblastic cells

Age-related bone loss may be a consequence of a lack of osteoblastic formation and/or function. In vitro, the osteoblastic response to 1,25(OH)2D3, an important regulator of osteoblastic function, appears to depend on the stage of osteoblastic maturation. In this study, we examined the response to 1,25(OH)2D3 of C-terminal type I procollagen (PICP), alkaline phosphatase (ALP), and osteocalcin (OC) secretion in primary cultures of osteoblastic cells from human trabecular bone (hOB). Forty-four bone samples were obtained from subjects undergoing knee arthroplastia, 20 aged 50-70 (64 +/- 5), and 24 >70 (73 +/- 2) years. Another 33 bone samples were obtained from subjects undergoing hip arthroplastia, 21 were aged 50-70 (64 +/- 4) and 12 >70 (75 +/- 5) years. Pooling knee and hip hOB cell cultures, we found that PICP secretion decreased after 1,25(OH)2D3 in hOB cells from the older group (>70 years). Treatment with 1,25(OH)2D3 increased ALP secretion in these cells only in the younger group (50-70 years), whereas it increased OC secretion in hOB cells in both age groups. By pooling hOB cell cultures from both age groups we found that knee hOB cells increased OC secretion, and decreased PICP secretion, after 1,25(OH)2D3. This metabolite also increased OC secretion in hip hOB cells. Considering the influence of donor age at the same skeletal site, 1,25(OH)2D3 was found to stimulate ALP secretion only in knee hOB cells in the younger group. In contrast, this metabolite decreased ALP secretion in hip hOB cells in the older group. PICP secretion decreased after 1,25(OH)2D3 only in hOB cells in the older group, at both skeletal sites. In age-matched cultures, OC secretion was lower in hip hOB cells compared with those from the knee in the older group, but was similar in these cell cultures from both skeletal sites in the younger group. OC secretion after 1,25(OH)2D3 stimulation did not show age differences in knee hOB cells, but was lower in hip hOB in the older group. In summary, our results demonstrate that the response of various osteoblastic markers to 1,25(OH)2D3 in primary cultures of hOB cells depends on the donor age and skeletal site of origin.

Renal expression of parathyroid hormone-related protein (PTHrP) and PTH/PTHrP receptor in a rat model of tubulointerstitial damage

BACKGROUND

PTHrP, which appears to act as a growth/differentiation factor in a variety of tissues, is present in the kidney; however, its role is unclear.

METHODS

The expression of PTHrP and the PTH/PTHrP receptor were investigated by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in the remnant kidney of uninephrectomized (UNX) rats after protein overloading [1 g/day of bovine serum albumin (BSA)].

RESULTS

Compared with UNX-control rats, proteinuria in BSA-overloaded animals was detected within the first 24 hours and increased during the entire study period (28 days). Kidney examination by light microscopy showed no significant renal lesions at day 1 of BSA treatment, whereas at days 8 and 28, tubular lesions, infiltration of mononuclear cells, and mesangial expansion were observed. PTHrP mRNA expression in the renal cortex was already increased at day 1 (fourfold) and plateaued between days 8 and 28 (12- and 15-fold, respectively) in BSA-overloaded animals compared with UNX-control rats. At day 8, immunohistochemical analysis with two different anti-PTHrP antibodies showed a dramatic increase of PTHrP staining in the damaged proximal and distal tubules from BSA-overloaded rats with respect to UNX-control rats. Moreover, intense PTHrP immunostaining was also observed in glomerular mesangial and endothelial cells in BSA-overloaded rats, but not in the UNX-control rats. A reciprocal decrease of PTH/PTHrP receptor mRNA and immunostaining, without significant changes in the cellular localization (proximal and distal tubule, and glomerular mesangial and epithelial cells) of the PTH/PTHrP receptor positivity was found to occur in the renal cortex of BSA-overloaded rats. At day 8, coinciding with the up-regulation of PTHrP, an increase in the angiotensin converting enzyme and preproendothelin-1 gene expression was observed in the renal cortex of BSA-overloaded rats compared with UNX-control rats.

CONCLUSIONS

These results indicate that PTHrP can be added to the group of genes that are up-regulated in proximal tubular cells in response to intense proteinuria. Our results, together with previous findings, suggest that the vasoactive hormones angiotensin II and endothelin-1 could participate in the PTHrP production in the renal cortex of BSA-overloaded rats. Further experiments are required to clarify the mechanisms of PTHrP up-regulation and its possible role in the response to renal damage in this animal model.

Comparison of two immunoradiometric assays for parathyroid hormone-related protein in the evaluation of cancer patients with and without hypercalcemia

Hypercalcemia is a common paraneoplastic syndrome due to the secretion by tumors of parathyroid hormone-related protein (PTHrP) and/or other osteolytic factors. In the present study, we have measured plasma PTHrP using two immunoradiometric assays for PTHrP, assay N (Nichols) and assay I (INCSTAR), recognizing the 1-86 domain of PTHrP, for the evaluation of malignancy-associated hypercalcemia. The study included 25 tumor patients with hypercalcemia (HCa) [corrected serum calcium (SCa) > or = 2.70 mmol/L], 20 normocalcemic patients with cancer (NCa), and ten healthy control subjects. Plasma PTHrP was either undetectable or within the respective normal range in the majority of NCa patients and in the control subjects, with both assays. Plasma PTHrP was increased in 13 and 15 of HCa cases with assay N and assay I, respectively. PTHrP was elevated in plasma in 5/6 (assay N) and 3/6 (assay I) HCa patients with squamous tumors. However, plasma PTHrP was high in only 2/9 (assay N) and 1/9 (assay I) HCa cases with hematological tumors. Less than 40% of HCa patients with bone metastases, and >75% of those without bone involvement, had elevated plasma PTHrP with both assays. Detectable plasma PTHrP and SCa were significantly correlated using assay N (p = 0.025) and assay I (p = 0.01), in the HCa group. A highly significant correlation (p <0.001) was found between detectable plasma PTHrP with both assays, and a high agreement between them based on simple kappa statistics (p < 0.001), in the latter group. Our results indicate that each assay may be similarly useful in detecting PTHrP hyperproduction in cancer patients.

Parathyroid hormone-related protein increases DNA synthesis in proximal tubule cells by cyclic AMP- and protein kinase C-dependent pathways

The present study was performed to characterize the possible involvement of cAMP synthesis and protein kinase C (PKC) activation in the DNA synthesis-stimulating effect of parathyroid hormone-related protein (PTHrP) in proximal tubule cells. We found that DNA synthesis was stimulated by 10 microM 8BrcAMP, and 1 microM Sp-cDBIMPS, two cAMP analogs, and also by 1 microM phorbol 12-myristate 13-acetate (PMA) and 100 microM 1,2-dioctanoyl-sn-glycerol, two PKC activators, and 10 nM [Cys23] human (h)PTHrP (24-35) amide in rabbit proximal tubule cells (PTC). Both Sp-cDBIMPS and PMA, at 1 microM, also increased DNA synthesis in SV40-immortalized mouse proximal tubule cells MCT. Human PTHrP (7-34) amide [PTHrP (7-34)] dose dependently stimulated DNA synthesis in a similar manner as [34Tyr]PTHrP (1-34) amide [PTHrP (1-34)], in PTC. PMA pre-treatment for 20 h, which downregulates PKC, completely blocked the effect induced by PTHrP (7-34), but not that of PTHrP (1-34), in the latter cells. In contrast, the same PMA pre-treatment abolished the DNA synthesis stimulation by PTHrP (1-34) and PTHrP (7-34) in MCT cells, which appear to have PTH receptors mainly coupled to phospholipase C and not adenylate cyclase. Our results indicate that the stimulatory effect of PTHrP on DNA synthesis in proximal tubule cells is mediated by a cAMP- and PKC-dependent mechanism.

Cyclosporine increases renal parathyroid hormone-related protein expression in vivo in the rat

BACKGROUND

Clinical use of cyclosporine (CsA) is limited by its known nephrotoxicity. Parathyroid hormone (PTH)-related protein (PTHrP) increases after acute renal ischemia and stimulates proliferation of renal cells in culture. Herein, we have examined whether the renal expression of PTHrP and its PTH/PTHrP receptor is affected by chronic CsA nephrotoxicity.

METHODS

Rats were randomly assigned to receive daily intramuscular injections of either CsA (25 mg/kg) or the same volume of the vehicle olive oil (control) for 3 weeks. At this time interval, under ether anesthesia, rat blood and kidneys were obtained for analytical determinations, and total RNA isolation or immunohistochemistry, respectively.

RESULTS

Serum urea was 11+/-2 and 6+/-1 mmol/L (P < 0.01) in CsA-treated and control rats, respectively. We found that PTH/PTHrP receptor mRNA was unchanged, but PTHrP mRNA, and also transforming growth factor-beta1 mRNA expression as positive control, was about twofold increased in the kidney of CsA-treated rats. This was accompanied by increased PTHrP immunostaining in renal cortical tubules, associated with tubule vacuolation.

CONCLUSION

This study demonstrates an up-regulation of PTHrP, associated with chronic CsA-induced nephrotoxicity. Our findings support a role for PTHrP in the CsA-injured kidney.

Comparison of antiproliferative effects of atrial natriuretic peptide and transforming growth factor beta on rabbit kidney proximal tubule cells

The effects of atrial natriuretic peptide (ANP) and transforming growth factor beta (TGF beta) on cell proliferation were investigated in rabbit kidney proximal tubule cells. At 48 h, each agonist inhibited cell growth dose dependently. Moreover, the antiproliferative effect of both factors together was greater than that of each factor alone. However, coincubation of a high concentration (100 nM) of ANP and epidermal growth factor (EGF) was found to induce cell hypertrophy. This hypertrophic effect induced by ANP in the presence of EGF was mimicked by 8-BrcGMP but not by various cAMP analogues, at 100 microM, and was independent of the tyrosine kinase inhibitor genistein (10 microM). However, it was inhibited by 100 pM TGF beta. These in vitro results suggest that the antiproliferative effects of ANP and TGF beta may be part of a mechanism to modulate the hyperplastic effect of EGF in the renal proximal tubule during compensatory kidney growth.

C-terminal parathyroid hormone-related protein inhibits proliferation and differentiation of human osteoblast-like cells

Parathyroid hormone-related protein (PTHrP) is synthesized by osteoblasts, although its local role in bone is not completely understood. The C-terminal (107-111) region of PTHrP seems to be a potent inhibitor of osteoblastic bone resorption. We studied the effect of this PTHrP domain on the proliferation and synthesis of osteoblastic markers in osteoblast-like cells from adult human bone. We found that the human (h)PTHrP(107-139) fragment, between 10 fM and 10 nM, inhibited 3H-thymidine incorporation into these cells. The antiproliferative effect of the latter fragment, or that of hPTHrP(107-111), was similar to that induced by [Tyr34] hPTHrP(1-34) amide, bovine PTH(1-34), and hPTHrP(1-141), while hPTHrP(38-64) amide was ineffective. Human PTHrP(7-34) amide, at 10 nM, and 1 microM phorbol-12-myristate-13-acetate also significantly decreased DNA synthesis in human osteoblast-like cells. Neither hPTHrP(7-34) amide nor hPTHrP(107-139), at 10 nM, stimulated protein kinase A (PKA) activity in these cells. Moreover, 100 nM H-89, a PKA inhibitor, did not eliminate the inhibitory effect of hPTHrP(107-139) on these cells' growth. However 100 nM calphostin C, a PKC inhibitor, blunted this effect of PTHrP(107-139). In addition to their antimitogenic effect, hPTHrP(107-139) and hPTHrP(107-111) inhibited basal and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-stimulated alkaline phosphatase activity in these cells. Both fragments, like 1,25(OH)2D3, decreased C-terminal type I procollagen secretion into the cell-conditioned medium, but osteocalcin secretion by these cells was unaffected by the C-terminal PTHrP fragments. These findings suggest that PTHrP may act as a local regulator of bone formation.

Antiproliferative effect of the C-terminal fragments of parathyroid hormone-related protein, PTHrP-(107-111) and (107-139), on osteoblastic osteosarcoma cells

The C-terminal region of parathyroid hormone-related protein (PTHrP) containing the sequence (107-111) appears to be a potent inhibitor of osteoclastic bone resorption. In the present study, we have investigated the effect of human (h)PTHrP (107-139) and hPTHrP (107-111)NH2 on the proliferation of osteoblastic rat osteosarcoma UMR 106 cells. We found that both C-terminal PTHrP peptides, like hPTHrP (1-141), were antimitogenic for these cells, between 1 pM and 10 nM. [Tyr34]hPTHrP (1-34)NH2 was as potent as these peptides but less effective as growth inhibitor in these cells. UMR 106 cells were found to produce and secrete immunoreactive PTHrP. Addition of anti-PTHrP neutralizing antibodies to C- and N-terminal epitopes of PTHrP increased the growth of these cells. Our data suggest that the antiproliferative effect of these C-terminal PTHrP analogs may be independent of cyclic adenosine 3':5'-monophosphate (cAMP) and mediated by protein kinase C. These findings support an autocrine role of PTHrP in bone metabolism.

Hypertrophy of rabbit proximal tubule cells is associated with overexpression of TGF beta

The expression of transforming growth factor beta (TGF beta) in proximal tubule cells from rabbit kidney cortex after uninephrectomy (UNX) was investigated. Cell protein and [3H]leucine incorporation in these cells were significantly increased, while cell number was decreased, at two weeks following UNX. At this time period after UNX, we found that proximal tubule cells showed a dramatic increase of cytoplasmic immunostaining with a pan-specific anti-TGF beta antibody. This was accompanied by a 3-fold increase in TGF beta 1 mRNA expression in these cells. Furthermore, proximal tubule cells from two-week uninephrectomized rabbits secrete about 2-fold higher TGF beta bioactivity to the cell conditioned medium compared to cells from sham-operated animals. Addition of anti-TGF beta 1, beta 2, beta 3 neutralizing antibody increased the growth of the former cells, and it abolished cell hypertrophy. These results indicate that hypertrophy of proximal tubule cells during compensatory renal growth is associated with overexpression of TGF beta.

Immunohistochemical detection of parathyroid hormone-related protein in a rare variant of hepatic neoplasm (sclerosing hepatic carcinoma)

Sclerosing hepatic carcinoma represents an uncommon subtype of hepatic malignancy, frequently associated with hypercalcemia. We applied immunohistochemistry using the avidin-biotin-complex technique to examine the presence of parathyroid hormone-related protein (PTHrP) in formalin-fixed and paraffin-embedded sections of tissue from a case of sclerosing hepatic carcinoma obtained at autopsy. Two polyclonal antibodies against the regions 24 to 35 and 107 to 111 of human PTHrP, and a monoclonal antibody that recognizes the human sequence 38 to 64 of this protein, were used. Preabsortion tests using the corresponding synthetic peptide as antigen were done with these antibodies. The neoplastic tissue displayed cytoplasmic immunostaining, diffuse with the antibodies against the amino- or carboxy-terminal regions of PTHrP, and with a predominant peripheral pattern when using the antibody to the midregion of the molecule. Tumor cells positive for PTHrP were also positive for hepatocellular markers cytokeratins 10, 17, and 18, but negative for chromogranin A. Our findings provide the first evidence for PTHrP production in the sclerosing subtype of hepatic carcinoma.