Effects of Strontium on the Physicochemical Characteristics of Hydroxyapatite

In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1 g/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20–100 g/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0–100 g/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr+Ca) ratios ranging from 0–60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100 g/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr+Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.     

Comparison of effect of treatment with etidronate and alendronate on lumbar bone mineral density in elderly women with osteoporosis

The purpose of this open-labeled prospective study was to compare the treatment effects of cyclical etidronate and alendronate on the lumbar bone mineral density (BMD), bone resorption, and back pain in elderly women with osteoporosis. Fifty postmenopausal women with osteoporosis, age ranging from 55 to 86 years (mean: 70.7 years), were randomly divided into two groups with 25 patients in each group: the cyclical etidronate group (etidronate 200 mg daily for 2 weeks every 3 months) and the alendronate group (5 mg daily). The BMD of the lumbar spine (L1-L4) measured by DXA, the urinary cross-linked N-terminal telopeptides of type I collagen (NTX) level measured by the enzyme-linked immunosorbent assay, and back pain evaluated by the face scale score were assessed at baseline, 6 months, and 12 months. There were no significant differences in baseline characteristics including age, body mass index, years since menopause, lumbar BMD, urinary NTX level, and face scale score between the two treatment groups. Etidronate treatment sustained the lumbar BMD following a reduction in the urinary NTX level and improved back pain, while alendronate treatment reduced the urinary NTX level more significantly, resulting in an increase in the lumbar BMD, and similarly improved back pain. No serious adverse events were observed in either group. This study confirmed that alendronate treatment had a greater efficacy than etidronate treatment in increasing the lumbar BMD through the reduction of bone resorption in elderly women with osteoporosis.     

Effects of bisphosphonates on joint damage and bone loss in rat adjuvant-induced arthritis

Objective and design: Examination of the effects of bisphosphonates on joint damage and generalized bone loss.Materials: Adjuvant-arthritis was induced by injection of Mycobacterium butyricum into the footpad of the right hind paw of Lewis rats (8 animals/group) on day 0.Treatment: Arthritic rats were treated with the vehicle (saline), etidronate or alendronate (subcutaneously, daily 5 times a week for 3 weeks from day 1 to day 21). Experiment-1: Etidronate (0.1, 0.5, 2.5, 12.5 mg/kg) or alendronate (0.02, 0.1, 0.5, 2.5 mg/kg), Experiment-2: Etidronate (2.5, 5, 10mg/ kg) or alendronate (0.001, 0.01, 0.1 mg/kg).Methods: In the adjuvant-injected side of the hind limbs, paw swelling was evaluated at 1-week intervals, and bone mineral density (BMD) in the proximal tibia, histopathology and radiographical findings in the tibio-tarsal region were evaluated at the time of sacrifice (on day 21).Results: In all treatment schedules, both bisphosphonates significantly prevented paw swelling and bone loss. Alendronate reduced paw swelling at higher doses (over 0.1 mg/ kg) compared with its effect on BMD decrease (over 0.001 mg/kg). In contrast, etidronate reduced paw swelling and joint damage at doses similar to those (over 2.5 mg/kg) prevented BMD decrease.Conclusions: Both etidronate and alendronate are effective in reducing arthritic damage, but their effective dose ranges for inflammatory responses and BMD decrease clearly differ; i.e., the etidronate dose ranges for anti-inflammatory and anti-resorptive effects are similar, whereas the dose range for anti-inflammatory effects of alendronate is 100-fold higher than that for its anti-resorptive effects.Received 21 January 2003; returned for revision 14 July 2003; accepted by M. Katori 15 August 2003     

Exercise-Trained Young Men Have Higher Calcium Absorption Rates and Plasma Calcitriol Levels Compared with Age-Matched Sedentary Controls

The effect of physical activity on human calcium (Ca) metabolism is still not completely understood. Thus, we investigated fractional Ca absorption using a stable strontium test (Fc₂₄₀), calciotropic hormones, and renal Ca excretion in 31 young men with a high activity level (GH) and in 26 age-matched sedentary control subjects (GL). Weekly hours spent on physical activity, obtained with a questionnaire were 15.0 ± 6.6 (GH) and 1.0 ± 1.4 (GL), respectively. Serum testosterone levels were significantly lower in GH compared with GL (P < 0.005). Dietary Ca intake (4-day food record) was twice as high in GH compared with GL men (P < 0.001). GH had significantly higher serum calcitriol levels and Fc₂₄₀ values than GL (P < 0.001 and P < 0.01, respectively). In a stepwise multiple regression analysis including serum levels of 25-hydroxyvitamin D, calcitriol, testosterone, and dietary Ca intake, only calcitriol was significantly correlated with Fc₂₄₀ (P= 0.017). Twenty-four hour renal Ca excretion was only slightly higher in GH compared with GL (P < 0.05). However, additional Ca losses might have occurred through the extensive sweating of GH, as indicated by a difference of 1.7 liter between fluid intake and renal fluid excretion (P < 0.001). In summary, we observed a higher fractional Ca absorption rate in physically active young men compared with sedentary controls which is probably mediated by calcitriol. The low testosterone serum levels of the athletes were obviously not a limiting factor in Ca absorption efficiency. An additional Ca retention might, however, only be obtained if absorbed Ca exceeded total obligatory Ca losses. Received: 30 September 1999 / Accepted: 22 March 2000     

Development and clinical trial of a novel bioactive bone cement

Strontium (Sr) and related compounds have become more attractive in the prevention and treatment of osteoporosis. Previously, we developed a novel bioactive bone cement which is mainly composed of strontium-containing hydroxyapatite (Sr-HA) filler and bisphenol A diglycidylether dimethacrylate (Bis-GMA) resin. This bone cement is superior to conventional polymethylmethacrylate (PMMA) bone cement in bioactivity, biocompatibility, and osseointegration. It also has shown sufficient mechanical strength properties for its use in percutaneous vertebroplasty (PVP) and total hip replacement (THR). In this paper, we review the in vitro, in vivo and clinical evidence for the effectiveness of this bioactive bone cement.     

Clinical usefulness of measurements of urinary deoxypyridinoline (DPD) in patients with postmenopausal osteoporosis receiving intermittent cyclical etidronate: advantage of free form of DPD over total DPD in predicting treatment efficacy

 Deoxypyridinoline (DPD) in urine, which reflects systemic bone resorption, is considered useful for assessing the effects of osteoporosis treatment. However, there are various methods of measuring DPD in urine but have been few comparative studies of the effectiveness of these methods. In this study, we investigated 94 postmenopausal women (63 patients administered with intermittent cyclical etidronate (ICE), and 31 control patients) focusing on total DPD and free DPD, measured by high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA), respectively. For other metabolic bone markers, i.e., tartrate-resistant acid phosphatase (TRAP), bone-specific alkaline phosphatase (BAP), and osteocalcin (OC), we also investigated the ability of these markers to predict increases in bone mineral density (BMD), by employing receiver operating characteristic (ROC) analysis in relation to increasing BMD following ICE therapy, and we determined the usefulness of the different metabolic bone markers, using the signal-noise ratio derived from the mean significant change (MSC), which is double the day-to-day coefficient of variation in healthy volunteers. In the same way, we defined a significant change in BMD as double the mean change in BMD for 6 months after the initiation of observation in the control group, and we used this value as the cutoff value for ROC analysis. It was found that the assessment of urinary DPD was useful for assessing the treatment efficacy of ICE, and the assessment of changes at week 12 of therapy was most effective. In order to recognize changes in metabolic bone markers when the MSC is considered as the cutoff value, it is useful to assess the change in total DPD by HPLC. However, in order to predict increases in BMD 6 months or more after the initiation of ICE, it seems more effective to measure free DPD by ELISA. We conclude, therefore, that the measurement of free DPD by ELISA is more useful, especially when treatment efficacy of ICE is clinically predicted in individual patients with osteoporosis. Received: July 27, 2002/Accepted: January 20, 2003 RID="*" ID="*" Offprint requests to: K. Nakatsuka     

Kinetics of calcium metabolism in lactation

The calcium accretion rate and the size of the exchangeable calcium pool was determined in rats between the 12th and 17th day of lactation after a single intraperitoneal injection of⁴⁷Ca and⁸⁵Sr. The serum specific activity and the retention of both radioactive isotopes in the whole body and tibia (shaft and ends) was determined. The single compartment kinetic model by Bauer was used for the analysis of data.The results show a decrease in the accretion rate and an increase in the exchangeable calcium pool in lactating rats as compared to unmated animals.

---

Zusammenfassung Die Geschwindigkeit der Calciumzunahme und die Größe des austauschbaren Calciumpools wurde bei Ratten zwischen dem 12. und 17. Tag der Lactation nach einer einmaligen intraperitonealen Injektion von⁴⁷Ca und⁸⁵Sr bestimmt. Die spezifische Aktivität beider radioaktiven Isotopen im Serum und ihre Retention im ganzen Körper und in der Tibia (Schaft und Epiphysen) wurden bestimmt. Das kinetische Modell von Bauer für ein Kompartiment wurde für die Datenanalyse verwendet.Die Resultate zeigen eine Verminderung der Zunahmegeschwindigkeit und eine Erhöhung des austauschbaren Calciumpools bei laktierenden Tieren, verglichen mit unbegatteten Ratten.

---

Résumé Le taux de dépôt du calcium et l'ampleur du calcium total échangeable sont déterminés chez le rat entre le 12ème et 17ème jour de lactation, après une injection intrapéritonéale unique de⁴⁷Ca et⁸⁵Sr. L'activité spécifique du sérum et la rétention des deux isotopes radioactifs dans l'organisme entier et le tibia (diaphyse et épiphyses) sont déterminées. L'analyse des résultats est réalisée à l'aide du modèle cinétique de Bauer à un compartiment unique. C'est ainsi qu'on observe une diminution du taux de dépôt et une augmentation du calcium total échangeable pendant la lactation.

     

Biochemical responses in cultured cells following exposure to SrCl2: potential relevance to the mechanism of action in pain palliation

⁸⁹SrCl₂ is currently used as a systemic radioactive palliative treatment for painful osseous metastases associated with an osteoblastic reaction in bone. However, the biological mechanism by which ⁸⁹SrCl₂ mediates pain palliation remains unclear. In this study, attempts were made to elucidate the mechanisms by which ⁸⁹SrCl₂ might influence pain at these sites. Both the direct radiotoxic effects of ⁸⁹SrCl₂ on cell viability and its influence on cellular biosynthetic activity were investigated. The direct radiotoxic effects of ⁸⁹SrCl₂ and X-rays were compared using the prostate carcinoma cell line, PC-3. Comparable effects upon PC-3 cell viability were seen in response to exposure to an equivalent dose given by ⁸⁹SrCl₂ and X-rays (2 Gy). Experiments to investigate the indirect action of ⁸⁹SrCl₂ exposure employed the MC3T3-E1 cell line and focused on their production of Prostaglandin E₂ (PGE₂) and interleukin-6 (IL-6). Exposure of the MC3T3-E1 cell line to ⁸⁹SrCl₂ resulted in an increased production of PGE₂ in a concentration-dependent manner. No increased PGE₂ production was seen by the MC3T3-E1 cells in response to X-ray exposure either in the presence or absence of SrCl₂. IL-6 was produced by the MC3T3-E1 cells in response to ⁸⁹SrCl₂ exposure via a PGE₂-mediated pathway. This study demonstrates the release of potent biochemical modifiers of bone turnover in response to the systemically applied radiotherapeutic ⁸⁹SrCl₂. This strongly suggests the mechanism of pain palliation by ⁸⁹SrCl₂ is likely to result from a complex interaction of direct and indirect radiation-induced effects.     

MTT比色法评价掺锶羟磷灰石固溶体细胞毒性

利用MTT比色法评价掺锶羟磷灰石固溶体（简称锶磷灰石）的细胞毒性。对自行合成含锶量克分子数比例分别为1％、5％、10％、100％的掺锶羟磷灰石用MTT比色法进行细胞毒性测试。结果表明不同含锶量锶磷灰石的细胞毒性评级均为1级,提示锶磷灰石无明显细胞毒性,掺锶量的多少对细胞相对增殖影响不明显。