EpCAM as multi-tumour target for near-infrared fluorescence guided surgery.

BACKGROUND: Evaluation of resection margins during cancer surgery can be challenging, often resulting in incomplete tumour removal. Fluorescence-guided surgery (FGS) aims to aid the surgeon to visualize tumours and resection margins during surgery. FGS relies on a clinically applicable imaging system in combination with a specific tumour-targeting contrast agent. In this study EpCAM (epithelial cell adhesion molecule) is evaluated as target for FGS in combination with the novel Artemis imaging system. METHODS: The NIR fluorophore IRDye800CW was conjugated to the well-established EpCAM specific monoclonal antibody 323/A3 and an isotype IgG1 as control. The anti-EpCAM/800CW conjugate was stable in serum and showed preserved binding capacity as evaluated on EpCAM positive and negative cell lines, using flow cytometry and cell-based plate assays. Four clinically relevant orthotopic tumour models, i.e. colorectal cancer, breast cancer, head and neck cancer, and peritonitis carcinomatosa, were used to evaluate the performance of the anti-EpCAM agent with the clinically validated Artemis imaging system. The Pearl Impulse small animal imaging system was used as reference. The specificity of the NIRF signal was confirmed using bioluminescence imaging and green-fluorescent protein. RESULTS: All tumour types could clearly be delineated and resected 72 h after injection of the imaging agent. Using NIRF imaging millimetre sized tumour nodules were detected that were invisible for the naked eye. Fluorescence microscopy demonstrated the distribution and tumour specificity of the anti-EpCAM agent. CONCLUSIONS: This study shows the potential of an EpCAM specific NIR-fluorescent agent in combination with a clinically validated intraoperative imaging system to visualize various tumours during surgery.

Near infrared fluorescence imaging for early detection, monitoring and improved intervention of diseases involving the joint.

Joints consist of different tissues, such as bone, cartilage and synovium, which are at risk for multiple diseases. The current imaging modalities, such as magnetic resonance imaging, Doppler ultrasound, X-ray, computed tomography and arthroscopy, lack the ability to detect disease activity before the onset of anatomical and significant irreversible damage. Optical in vivo imaging has recently been introduced as a novel imaging tool to study the joint and has the potential to image all kinds of biological processes. This tool is already exploited in (pre)clinical studies of rheumatoid arthritis, osteoarthritis and cancer. The technique uses fluorescent dyes conjugated to targeting moieties that recognize biomarkers of the disease. This review will focus on these new imaging techniques and especially where Near Infrared (NIR) fluorescence imaging has been used to visualize diseases of the joint. NIR fluorescent imaging is a promising technique which will soon complement established radiological, ultrasound and MRI imaging in the clinical management of patients with respect to early disease detection, monitoring and improved intervention.

Intraoperative fluorescence delineation of head and neck cancer with a fluorescent anti-epidermal growth factor receptor nanobody.

Intraoperative near-infrared (NIR) fluorescence imaging is a technology with high potential to provide the surgeon with real-time visualization of tumors during surgery. Our study explores the feasibility for clinical translation of an epidermal growth factor receptor (EGFR)-targeting nanobody for intraoperative imaging and resection of orthotopic tongue tumors and cervical lymph node metastases. The anti-EGFR nanobody 7D12 and the negative control nanobody R2 were conjugated to the NIR fluorophore IRDye800CW (7D12-800CW and R2-800CW). Orthotopic tongue tumors were induced in nude mice using the OSC-19-luc2-cGFP cell line. Tumor-bearing mice were injected with 25 µg 7D12-800CW, R2-800CW or 11 µg 800CW. Subsequently, other mice were injected with 50 or 75 µg of 7D12-800CW. The FLARE imaging system and the IVIS spectrum were used to identify, delineate and resect the primary tumor and cervical lymph node metastases. All tumors could be clearly identified using 7D12-800CW. A significantly higher tumor-to-background ratio (TBR) was observed in mice injected with 7D12-800CW compared to mice injected with R2-800CW and 800CW. The highest average TBR (2.00 ± 0.34 and 2.72 ± 0.17 for FLARE and IVIS spectrum, respectively) was observed 24 hr after administration of the EGFR-specific nanobody. After injection of 75 µg 7D12-800CW cervical lymph node metastases could be clearly detected. Orthotopic tongue tumors and cervical lymph node metastases in a mouse model were clearly identified intraoperatively using a recently developed fluorescent EGFR-targeting nanobody. Translation of this approach to the clinic would potentially improve the rate of radical surgical resections.

Inhibition of Gsk3ß in cartilage induces osteoarthritic features through activation of the canonical Wnt signaling pathway.

OBJECTIVE: In the past years, the canonical Wnt/ß-catenin signaling pathway has emerged as a critical regulator of cartilage development and homeostasis. In this pathway, glycogen synthase kinase-3ß (GSK3ß) down-regulates transduction of the canonical Wnt signal by promoting degradation of ß-catenin. In this study we wanted to further investigate the role of Gsk3ß in cartilage maintenance. DESIGN: Therefore, we have treated chondrocytes ex vivo and in vivo with GIN, a selective GSK3ß inhibitor. RESULTS: In E17.5 fetal mouse metatarsals, GIN treatment resulted in loss of expression of cartilage markers and decreased chondrocyte proliferation from day 1 onward. Late (3 days) effects of GIN included cartilage matrix degradation and increased apoptosis. Prolonged (7 days) GIN treatment resulted in resorption of the metatarsal. These changes were confirmed by microarray analysis showing a decrease in expression of typical chondrocyte markers and induction of expression of proteinases involved in cartilage matrix degradation. An intra-articular injection of GIN in rat knee joints induced nuclear accumulation of ß-catenin in chondrocytes 72 h later. Three intra-articular GIN injections with a 2 days interval were associated with surface fibrillation, a decrease in glycosaminoglycan expression and chondrocyte hypocellularity 6 weeks later. CONCLUSIONS: These results suggest that, by down-regulating ß-catenin, Gsk3ß preserves the chondrocytic phenotype, and is involved in maintenance of the cartilage extracellular matrix. Short term ß-catenin up-regulation in cartilage secondary to Gsk3ß inhibition may be sufficient to induce osteoarthritis-like features in vivo.

Near-infrared fluorescence imaging in patients undergoing pancreaticoduodenectomy.

BACKGROUND: Intraoperative visualization of pancreatic tumors has the potential to improve radical resection rates. Intraoperative visualization of the common bile duct and bile duct anastomoses could be of added value. In this study, we explored the use of indocyanine green (ICG) for these applications and attempted to optimize injection timing and dose. METHODS: Eight patients undergoing a pancreaticoduodenectomy were injected intravenously with 5 or 10 mg ICG. During and after injection, the pancreas, tumor, common bile duct and surrounding organs were imaged in real time using the Mini-FLARE™ near-infrared (NIR) imaging system. RESULTS: No clear tumor-to-pancreas contrast was observed, except for incidental contrast in 1 patient. The common bile duct was clearly visualized using NIR fluorescence, within 10 min after injection, with a maximal contrast between 30 and 90 min after injection. Patency of biliary anastomoses could be visualized due to biliary excretion of ICG. CONCLUSION: No useful tumor demarcation could be visualized in pancreatic cancer patients after intravenous injection of ICG. However, the common bile duct and biliary anastomoses were clearly visualized during the observation period. Therefore, these imaging strategies could be beneficial during biliary surgery in cases where the surgical anatomy is aberrant or difficult to identify.

'In vivo' optical approaches to angiogenesis imaging.

In recent years, molecular imaging gained significant importance in biomedical research. Optical imaging developed into a modality which enables the visualization and quantification of all kinds of cellular processes and cancerous cell growth in small animals. Novel gene reporter mice and cell lines and the development of targeted and cleavable fluorescent "smart" probes form a powerful imaging toolbox. The development of systems collecting tomographic bioluminescence and fluorescence data enabled even more spatial accuracy and more quantitative measurements. Here we describe various bioluminescent and fluorescent gene reporter models and probes that can be used to specifically image and quantify neovascularization or the angiogenic process itself.

Sclerostin: current knowledge and future perspectives.

In recent years study of rare human bone disorders has led to the identification of important signaling pathways that regulate bone formation. Such diseases include the bone sclerosing dysplasias sclerosteosis and van Buchem disease, which are due to deficiency of sclerostin, a protein secreted by osteocytes that inhibits bone formation by osteoblasts. The restricted expression pattern of sclerostin in the skeleton and the exclusive bone phenotype of good quality of patients with sclerosteosis and van Buchem disease provide the basis for the design of therapeutics that stimulate bone formation. We review here current knowledge of the regulation of the expression and formation of sclerostin, its mechanism of action, and its potential as a bone-building treatment for patients with osteoporosis.

Synergistic effect of bisphosphonate and docetaxel on the growth of bone metastasis in an animal model of established metastatic bone disease.

Bisphosphonates decrease bone resorption and reduce significantly the rate of skeletal complications in patients with metastatic bone disease. Bisphosphonates have also been shown to exhibit antitumor activity in vitro but in vivo results have been equivocal. In the present study, we investigated the effects of bisphosphonate treatment alone or in combination with the cytostatic docetaxel on the growth of breast cancer cells in bone. Tumor gowth was studied in an athymic nude mice model inoculated with MDA-231-B/luc+ breast cancer cells. Two days after the inoculation, mice were treated with risedronate, zolendronate or docetaxel alone or with a combination of risedronate and docetaxel. Bone destruction and tumor growth were evaluated radiographically, histologically and by whole-body bioiluminescent reporter imaging (BLI). Five week treatment with high doses risedronate or zoledronate (37.5-150 microg/kg, 5 times/week), fully protected the bones from osteolysis, but did not affect tumour growth. Docetaxel (2, 4, and 8 mg/kg, 2 times/week) inhibited tumour growth dose-dependently and after 5 weeks treatment with the highest dose, there was no detectable tumour in bone. The combination of a dose of docetaxel (4 mg/kg) that demonstrated only a minimal effect on tumour growth, with risedronate (150 microg/kg), protected bone integrity and nearly completely inhibited the growth of the cancer cells. Risedronate and docetaxel act synergistically to protect bone and decrease tumour burden in an animal model of established bone metastases from breast cancer cells.

Novel mutations in the parathyroid hormone (PTH)/PTH-related peptide receptor type 1 causing Blomstrand osteochondrodysplasia types I and II.

CONTEXT: The PTH/PTHrP receptor type 1 (PTHR1) has a key role in endochondral ossification, which is emphasized by diseases resulting from mutations in the PTHR1 gene. Among these diseases is Blomstrand osteochondrodysplasia (BOCD). OBJECTIVE: BOCD can be divided into two types, depending on the severity of the skeletal abnormalities. The molecular basis for this heterogenic presentation is unknown. DESIGN AND PATIENTS: We performed mutation analysis in two families with type I and in three families with the less severe form of BOCD type II. RESULTS: In one of the type I BOCD cases, a homozygous nonsense mutation (R104X) was found, resulting in a truncated PTHR1. In the second type I BOCD case, no mutation was found. A homozygous nucleotide change (intron M4+27C>T) was demonstrated in one of the type II BOCD cases creating a novel splice site. In dermal fibroblasts of the patient, this novel splice site was preferentially used, resulting in an aberrant transcript. The wild-type transcript remained, however, present, albeit at low levels. In the other two families with type II BOCD, a previously identified homozygous missense mutation (P132L) was found. Functional analysis demonstrated that the P132L mutant had low residual activity. CONCLUSIONS: In combination with data presented in literature, we conclude that type I BOCD is caused by a complete inactivation of the PTHR1, whereas low levels of residual activity due to a near complete inactivation of the PTHR1 result in the relatively milder presentation of type II BOCD.

Preclinical uPAR-targeted multimodal imaging of locoregional oral cancer.

OBJECTIVES: Establishing adequate resection margins and lymphatic mapping are crucial for the prognosis of oral cancer patients. Novel targeted imaging modalities are needed, enabling pre- and intraoperative detection of tumour cells, in combination with improved post-surgical examination by the pathologist. The urokinase-receptor (uPAR) is overexpressed in head and neck cancer, where it is associated with tumour progression and metastasis. MATERIAL AND METHODS: To determine suitability of uPAR for molecular imaging of oral cancer surgery, human head and neck tumours were sectioned and stained for uPAR to evaluate the expression pattern compared to normal mucosa. Furthermore, metastatic oral squamous carcinoma cell line OSC-19 was used for targeting uPAR in in vivo mouse models. Using anti-uPAR antibody ATN-658, equipped with a multimodal label, the in vivo specificity was investigated and the optimal dose and time-window were evaluated. RESULTS: All human oral cancer tissues expressed uPAR in epithelial and stromal cells. Hybrid ATN-658 clearly visualized tongue tumours in mice using either NIRF or SPECT imaging. Mean fluorescent TBRs over time were 4.3±0.7 with the specific tracer versus 1.7±0.1 with a control antibody. A significant difference in TBRs could be seen between 1nmol (150µg) and 0.34nmol (50µg) dose groups (n=4, p<0.05). Co-expression between BLI, GFP and the NIR fluorescent signals were seen in the tongue tumour, whereas human cytokeratin staining confirmed presence of malignant cells in the positive cervical lymph nodes. CONCLUSION: This study shows the applicability of an uPAR specific multimodal tracer in an oral cancer model, combining SPECT with intraoperative guidance.

Accelerated atherosclerosis and calcification in vein grafts: a study in APOE*3 Leiden transgenic mice.

Vein grafts fail due to development of intimal hyperplasia and accelerated atherosclerosis. Many murine genetic models in which genes are overexpressed, deleted, or mutated have been introduced recently. Therefore, mouse models are very well suited to dissect the relative contribution of different genes in the development of accelerated atherosclerosis. In the present study, we evaluated whether accelerated atherosclerosis in human vein grafts could be mimicked in hypercholesterolemic APOE*3 Leiden transgenic mice. Venous bypass grafting was performed in the carotid artery in APOE*3 Leiden mice fed either a standard chow diet or a high cholesterol-rich diet for 4 weeks. At several time points (0 hour to 28 days), mice were euthanized and the morphology of the vein grafts was analyzed. In normocholesterolemic mice, vein graft thickening up to 10-fold original thickness, predominantly consisting of alpha-smooth muscle cell actin-positive cells, was observed after 28 days. In hypercholesterolemic mice, accelerated atherosclerosis with accumulation of lipid-loaded foam cells was observed within 7 days after surgery. This accelerated atherosclerosis progressed in time and resulted in significant increase in vein graft thickening up to 50 times original thickness with foam cell-rich lesions and calcification within 28 days after surgery. The atherosclerotic lesions observed in these murine grafts show high morphological resemblance with the atherosclerotic lesions observed in human vein grafts. This accelerated, diet-dependent induction of atherosclerotic-like lesions in murine vein grafts provides a valuable tool in evaluating the mechanisms of accelerated atherosclerosis and therapeutic interventions of vein graft disease.

Characterization and evaluation of the artemis camera for fluorescence-guided cancer surgery.

PURPOSE: Near-infrared (NIR) fluorescence imaging can provide the surgeon with real-time visualization of, e.g., tumor margins and lymph nodes. We describe and evaluate the Artemis, a novel, handheld NIR fluorescence camera. PROCEDURES: We evaluated minimal detectable cell numbers (FaDu-luc2, 7D12-IRDye 800CW), preclinical intraoperative detection of sentinel lymph nodes (SLN) using indocyanine green (ICG), and of orthotopic tongue tumors using 7D12-800CW. Results were compared with the Pearl imager. Clinically, three patients with liver metastases were imaged using ICG. RESULTS: Minimum detectable cell counts for Artemis and Pearl were 2 × 10(5) and 4 × 10(4) cells, respectively. In vivo, seven SLNs were detected in four mice with both cameras. Orthotopic OSC-19-luc2-cGFP tongue tumors were clearly identifiable, and a minimum FaDu-luc2 tumor size of 1 mm(3) could be identified. Six human malignant lesions were identified during three liver surgery procedures. CONCLUSIONS: Based on this study, the Artemis system has demonstrated its utility in fluorescence-guided cancer surgery.

Exposure of KS483 cells to estrogen enhances osteogenesis and inhibits adipogenesis.

Osteoblasts and adipocytes arise from a common progenitor cell in bone marrow. Whether estrogen directly regulates the progenitor cells differentiating into osteoblasts or adipocytes remains unknown. Using a mouse clonal cell line KS483 cultured in charcoal-stripped fetal bovine serum (FBS), we showed that 17beta-estradiol (E2) stimulates the differentiation of progenitor cells into osteoblasts and concurrently inhibits adipocyte formation in an estrogen receptor (ER)-dependent way. E2 increased alkaline phosphate (ALP) activity and nodule formation and stimulated messenger RNA (mRNA) expression of core-binding factor alpha-1 (Cbfa1), parathyroid hormone/parathyroid hormone-related protein receptors (PTH/PTHrP-Rs), and osteocalcin. In contrast, E2 decreased adipocyte numbers and down-regulated mRNA expression of peroxisome proliferator-activated receptor-gamma (PPARgamma)2, adipocyte protein 2 (aP2), and lipoprotein lipase (LPL). Furthermore, the reciprocal control of osteoblast and adipocyte differentiation by E2 was observed also in the presence of the adipogenic mixture of isobutylmethylxanthine, dexamethasone, and insulin. Immunohistochemical staining showed that ERalpha and ERbeta were present in osteoblasts and adipocytes. A new mouse splice variant ERbeta2 was identified, which differed in two amino acid residues from the rat isoform. E2 down-regulated mRNA expression of ERalpha, ERbeta1, and ERbeta2. The effects of E2 are not restricted to the KS483 cell line because similar results were obtained in mouse bone marrow cell cultures. Our results indicate that estrogen, in addition to stimulation of osteogenesis, inhibits adipogenesis, which might explain the clinical observations that estrogen-deficiency leads to an increase in adipocytes.

Sex steroid metabolism in the tibial growth plate of the rat.

To assess whether growth plate-specific production of sex steroids is possible, we have surveyed the presence of several key-enzymes involved in androgen and estrogen metabolism in the tibial growth plate of female and male rats during development. Using in situ hybridization, mRNAs of aromatase p450, type I and II 17beta-hydroxysteroid dehydrogenase (HSD), steroid sulfatase (STS), and 5alpha-reductase were detected in proliferating and hypertrophic chondrocytes of the growth plate. The former three were strongly up-regulated around sexual maturation (7 wk), whereas the latter two were expressed at a relatively constant level during development. These data were supported by measuring aromatase, type I 17beta-HSD, and STS enzyme activities in chondrocytes collected from tibial growth plates at 1 and 7 wk of age. Of the enzymes studied, there were minor differences between the sexes in aromatase and 5alpha-reductase expression only. In conclusion, our findings clearly indicate the presence of various enzymes involved in sex steroid metabolism in the tibial growth plate, especially in sexually maturing rats, a timepoint at which sex steroids have major effects on longitudinal growth. Our data suggest that intracrinology in the rat growth plate can occur and may be a major source of local sex steroid delivery.

Bisphosphonates suppress bone resorption by a direct effect on early osteoclast precursors without affecting the osteoclastogenic capacity of osteogenic cells: the role of protein geranylgeranylation in the action of nitrogen-containing bisphosphonates on osteoclast precursors.

Nitrogen-containing bisphosphonates (NBps) are taken up by osteoclasts and inhibit farnesyl pyrophosphate synthase, an enzyme of the mevalonate pathway. There is evidence, however, that cells other than mature osteoclasts, like osteoclast precursors and osteoblasts, are also involved in the action of Bps on bone resorption in vitro. To examine this issue further, we developed a new in vitro model, which allows the study of the effects of additives on early osteoclast precursors. In this model, osteogenic cells are essential for osteoclastogenesis. The model consists of 15-day-old fetal mouse metatarsals. At time of explantation, these bone rudiments do not yet contain a mineralized matrix or osteoclasts; only early osteoclast precursors are present in the perichondrium. During culture and after the addition of Nabeta-glycerolphosphate, the bones form a mineralized matrix that is consequently resorbed by osteoclasts that develop from their precursors. Short treatment of these explants with Bps, before the formation of a mineralized matrix, resulted in a subsequent dose-dependent inhibition of bone resorption. The relative potencies of eight Bps to suppress resorption were comparable with those observed after the addition of Bps after the formation of a mineralized matrix, the natural target of Bps. In addition, the effects of the NBp olpadronate, but not of clodronate, on osteoclastic resorption, could be partly reversed by geranylgeraniol. Results indicate that Bps can suppress osteoclastic resorption in vitro by a direct action on very early osteoclast precursors at the bone surface, and not by affecting the osteoclastogenic capacity of osteogenic cells. Moreover, the mechanism of action of the NBp olpadronate, but not clodronate, on early tartrate-resistant acid phosphatase-negative osteoclast precursors involves inhibition of protein geranylgeranylation, indicating a molecular mechanism similar to that established for mature osteoclasts.

Differentiation of murine preosteoblastic KS483 cells depends on autocrine bone morphogenetic protein signaling during all phases of osteoblast formation.

In this study, we examine the role of bone morphogenetic protein (BMP) signaling during differentiation of the murine preosteoblastic KS483 cell line, which formed alkaline phosphatase (ALP)-positive and mineralized nodules during a 3 week culture period. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) demonstrated the presence of various BMPs (BMP-2, -3, -4, -6, -7, and -8A and -8B), BMP type I and II receptors (ALK2, ALK3, ALK4, BMPR-II, and ActR-IIA and -IIB), BMP antagonists (DAN, gremlin, chordin, cerberus, noggin, and tsg), and Smads 1-8. mRNA expression of these genes did not change during differentiation, except for BMP-3, BMP-8a, and noggin. BMP-3 increased gradually, particularly in the matrix formation phase; BMP-8a was induced from the onset of matrix maturation and mineralization, in parallel to the expression of osteocalcin; and noggin tended to decline during the mineralization phase. Treatment of KS483 cells with the BMP antagonists noggin or soluble truncated BMPR-IA, either continuously or during distinct periods of osteoblast differentiation; that is, matrix formation or matrix maturation and mineralization phase, decreased ALP-positive and mineralized nodule area independent of the phase of osteoblast differentiation. Notably, the antagonists inhibited mineralization of already existing nodules. Similarly, BMP-4 stimulated differentiation not only at the beginning of the culture period, but also at late stages of differentiation. These data indicate that autocrine BMP signaling is involved in KS483 osteoblastic differentiation not only during the early phase of differentiation, but also during matrix maturation and mineralization. The different expression patterns of components of BMP signaling in the KS483 cells suggest distinct functions of individual BMPs during osteoblast differentiation. In summary, our data suggest that BMP activity is required not only for initiation of osteoblast differentiation and further development of early osteoblasts, but is also involved in late-stage osteoblast differentiation and matrix mineralization.

Gender differences in expression of androgen receptor in tibial growth plate and metaphyseal bone of the rat.

In this study, we investigate the expression of the androgen receptor (AR) in the tibial growth plate and metaphyseal bone of male and female rats at the mRNA and protein level. Using in situ hybridization and immunohistochemistry, AR mRNA and protein were demonstrated in proliferating and early hypertrophic chondrocytes in the growth plate of 1-, 4-, and 7-week-old male and female rats. Immunostaining for AR was observed both in the nucleus and the cytoplasm. After sexual maturation at 12 and 16 weeks of age, AR expression decreased in both genders and was confined to a small rim of prehypertrophic chondrocytes. In female rats of 40 weeks of age, this expression pattern was still visible. In most age groups there was a tendency toward an increased AR mRNA expression in male vs. female rats except in the 7-week-old animals. At the protein level, sexually maturing 7-week-old male rats demonstrated a higher staining intensity compared to their female counterparts. At this stage, AR staining in the males was mainly confined to the nucleus, whereas in females staining was predominantly found in the cytoplasm. In the tibial metaphysis, AR mRNA was detected in lining cells, osteoblasts, osteocytes, and osteoclasts at all stages of development. At the protein level, a similar expression pattern was observed, except for an absence of immunostaining in the lining cells. The staining was both nuclear and cytoplasmic. In most age groups, mRNA and protein signals were higher in males compared with females. We have demonstrated the presence of AR mRNA and protein in the tibial growth plate and the underlying metaphyseal bone during development of the rat. In male rats, the presence of higher messenger and protein staining intensities, as well as preferential nuclear staining during sexual maturation, suggests that direct actions of androgens in chondrocytes and in bone forming cells may be involved in establishing the gender differences in the skeleton.

Expression of estrogen receptor alpha and beta in the epiphyseal plate of the rat.

In this study we examine the spatial and temporal expression of estrogen receptor (ER) alpha and beta mRNA and protein in the tibial growth plate of the rat after birth, as well as the hormonal regulation of their expression. Using in situ hybridization and immunohistochemistry, we demonstrated ER alpha and ER beta mRNA and protein in tibial growth plates from 1 to 40 weeks after birth. ER alpha and beta mRNA and protein were localized in late proliferating and early hypertrophic chondrocytes during early life (1 and 4 weeks of age), whereas the immunohistochemistry also showed staining for ER alpha and beta in the resting cells. A similar expression pattern was observed during sexual maturation (7 weeks of age) except that ER beta mRNA was also detected in early proliferating chondrocytes. After sexual maturation (from 12 up to 40 weeks of age) ER alpha and beta mRNA and protein expression was confined to late proliferating and early hypertrophic chondrocytes. Apart from a relatively higher ER alpha mRNA expression in males after sexual maturation, we did not detect differences in expression of ERs between genders. Expression of ER beta mRNA in epiphyseal plates was increased in growth-retarded hypophysectomized rats compared with controls. Administration of growth hormone (GH) did not reverse the increased ER expression to normal. These data suggest that ER alpha and beta are coexpressed in growth plates of the rat after birth and that the level of expression of ERs in these tissues is hormonally regulated. Furthermore, our data indicate that the absence of growth-plate closure in the rat cannot be explained by disappearance of ER alpha expression during sexual maturation per se.

Differentiating the mechanisms of antiresorptive action of nitrogen containing bisphosphonates.

Bisphosphonates (BPS) inhibit bone resorption and are divided into two classes according to their chemical structure and mechanism of action: nonnitrogen containing BPS such as etidronate and clodronate that are of low potency and inhibit osteoclast function via metabolism into toxic ATP-metabolites and nitrogen-containing BPS (NBPS), such as alendronate and risedronate that inhibit the enzyme of the mevalonate biosynthetic pathway farnesyl pyrophosphate synthase (FPPS), resulting in inhibition of the prenylation of small GTP-binding proteins in osteoclasts and disruption of their cytoskeleton. Previously, studies in various cell types suggested, however, that pamidronate functions by mechanism(s) additional or independent of the mevalonate pathway. To examine if such mechanism(s) are also involved in the action of NBPS on osteoclastic bone resorption, we examined the action of alkyl and heterocyclic NBPS with close structural homology on FPPS/isopentenyl pyrophosphate isomerase (IPPI) activity, on osteoclastic resorption, and on reversibility of this effect with GGOH. As expected, both pamidronate and alendronate suppressed bone resorption and FPPS/IPPI activity, the latter with greater potency than the first. Surprisingly, however, unlike alendronate, the antiresorptive effect of pamidronate was only partially reversible with GGOH, indicating the involvement of mechanism(s) of action additional to that of suppression of FPPS. Comparable results were obtained with the heterocyclic NBP NE-21650, a structural analog of risedronate. Thus, despite an effect on FPPS, the actions on bone resorption of some NBPS may involve mechanisms additional to suppression of FPPS. These findings may lead to identification of additional pathways that are important for bone resorption and may help to differentiate among members of the NBP class which are currently distinguished only according to their potency to inhibit bone resorption.

Expression of estrogen receptors and enzymes involved in sex steroid metabolism in the rat tibia during sexual maturation.

Estrogens are essential for bone mass accrual but their role before sexual maturation has remained elusive. Using in situ hybridization and immunohistochemistry, we investigated the expression of both estrogen receptor (ER) alpha and beta mRNA and protein as well as several mRNAs coding for enzymes involved in sex steroid metabolism (aromatase, type I and II 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD), steroid sulfatase (STS) and type I 5 alpha-reductase) on sections of tibial metaphyses before (1- and 4-week-old), during (7-week-old) and after (16-week-old) sexual maturation in female and male rats. ER alpha and ER beta mRNA and protein were detected in metaphyseal bone in lining cells, osteoblasts, osteoclasts and some osteocytes with no apparent differences in expression during development or between the sexes. In contrast, aromatase, type I and II 17 beta-HSD and type I 5 alpha-reductase mRNAs were first detected in osteoblasts, osteoclasts and occasionally in osteocytes from sexual maturation (7-week-old rat) and onwards. Only STS was present before sexual maturation. To study the significance of ER alpha and beta expression in bone before sexual maturation when circulating sex steroid levels are low, 26-day-old female and male rats underwent gonadectomy or 17 beta-estradiol (E(2)) supplementation (0.5 mg/21 days) during 3 weeks. Following gonadectomy, trabecular bone volume (TBV) was lower in males (P=0.03) and there was a trend towards reduction in females (P=0.057). E(2) supplementation increased tibial TBV compared with controls in both genders as assessed by Masson-Goldner staining. These data suggest that the presence of ERs in bone cells before sex maturation might be of significance for bone mass accrual. Furthermore, based on the mRNA expression of the crucial enzymes aromatase and type I 17 beta-HSD, we suggest that bone cells in the tibial metaphysis acquire the intrinsic capacity to metabolize sex steroids from sexual maturation onwards. This process may contribute to the beneficial effects of estrogen on bone mass accrual, possibly by intracrinology.