1,25 dihydroxyvitamin D3 alone or in combination with parathyroid hormone does not increase bone mass in young rats

Summary Parathyroid hormone (PTH) alone is known to increase bone mass, but clinical studies of osteoporotic men suggest that when 1,25 dihydroxyvitamin D₃ (1,25(OH)₂D₃) is given in combination with PTH, the effect on bone growth is enhanced. To determine if 1,25(OH)₂D₃ alone would stimulate bone growth, young male rats were given daily subcutaneous injections of either vehicle or 2.5, 5, 10, or 20 ng 1,25(OH)₂D₃ per 100 g body weight for 30 days. To determine if 1,25(OH)₂D₃ would augment the PTH anabolic response, rats were given daily subcutaneous injections of either vehicle for 12 days; or 4 μg/100 g hPTH alone or in combination with 5 ng/100 g 1,25(OH)₂D₃; or 8 μg/100 g hPTH alone or in combination with 5 ng/100 g 1,25(OH)₂D₃. Calcium (Ca), dry weight (DW), and hydroxyproline (Hyp) of the distal femur; the rate of mineralization in the metaphysis of the proximal tibia; and serum calcium and phosphate were measured. Low normocalcemic doses of 1,25(OH)₂D₃ did not significantly stimulate bone growth. 1,25(OH)₂D₃ did not augment the PTH-stimulated anabolic effect in young male rats. Low doses (2.5 and 5 ng) of 1,25(OH)₂D₃ were not hypercalcemic, and there was no increase in total bone calcium or dry weight although the 5 ng dose increased trabecular bone calcium. 1,25(OH)₂D₃ at 10 and 20 ng increased trabecular bone DW and Hyp, but mineralization was impaired and rats were hypercalcemic. 1,25(OH)₂D₃ in combination with PTH did not augment the PTH stimulation of bone growth as trabecular and cortical bone Ca, DW, and HYP were not increased in rats given both hPTH and 1,25(OH)₂D₃ compared with values for rats treated with hPTH alone.     

Maintenance of vertebral body bone mass and strength created by human parathyroid hormone treatment in ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone (1-84) (hPTH) followed by maintenance administration of 17beta-estradiol (E2), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on vertebral body bone mineral density (BMD) and bone strength in ovariectomized (ovx) rats. Eight groups of ovx (219 rats) and one group of intact female rats (48 rats) were left untreated for 11 weeks (age 3.5 months at the beginning). For the following 12 weeks, four ovx groups received subcutaneous injections of hPTH (75 microg/kg per day, 3 days/week) and four groups received vehicle. Treatments were then changed to: E2 (10 microg/kg per day, 2 days/week); Ris (3 microg/kg per day, 3 days/week); LowPTH (25 microg/kg per day, 3 days/week); or vehicle for 36 weeks. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). The endpoints were vertebral body BMD, ultimate stress (Ultstr), and moduli of elasticity from compression tests (ModM), and from ultrasound tests (ModUS). Ovariectomy resulted in lower BMD (p < 0.001). The hPTH treatment for 12 weeks restored BMD to the level of intact rats. Ultstr and ModUS followed a similar pattern, but the ovx-induced Ultstr was not significant (p = 0.073, ModUS: p = 0.003), nor was the hPTH-induced increase in ModUS (p = 0.131, Ultstr: p = 0.02). After hPTH withdrawal, BMD, Ultstr, and ModUS levels were not different from levels in ovx animals. In Ris-treated rats pretreated with hPTH, BMD (weeks 24 and 48, p < 0.002) and ModUS (week 24, p = 0.018) values were greater than in ovx animals. In LowPTH-treated rats pretreated with hPTH, BMD (weeks 24 and 48, p < 0.001) and Ultstr (week 48, p = 0.005) were greater than in ovx animals. In E(2)-treated rats pretreated with hPTH, BMD was greater than in ovx rats at week 24 (p = 0.009), but did not differ at weeks 36-48. Neither Ultstr nor ModUS in E(2)-treated rats differed significantly from ovx rats at any timepoint. Of the agents and dosing regimens used, we conclude that the hPTH-related vertebral bone mass gain in ovx rats can be maintained for up to 36 weeks with risedronate and low-dose hPTH treatment. Bone strength is maintained by treatment with low-dose hPTH, but only partially maintained with risedronate.     

Effects of separate and combined therapy with growth hormone and parathyroid hormone on lumbar vertebral bone in aged ovariectomized osteopenic rats

Previous studies have demonstrated that growth hormone (GH) has a marked anabolic effect on cortical bone, and parathyroid hormone (PTH) has been shown to increase cancellous bone markedly and cortical bone to some extent in ovariectomized (ovx) rats. Combined therapies mostly focused on combining a bone anabolic agent with an antiresorptive agent. The following study was carried out to examine the efficacy of combined therapy with GH and PTH, two bone anabolic agents in rebuilding bone after loss due to ovariectomy in lumbar vertebrae, which contain both cortical and cancellous bones. Twelve-month-old female F344 rats were divided into five groups: sham + solvent vehicle, ovx + solvent vehicle, ovx + GH (2.5 mg/kg/day), ovx + PTH (80 microg/kg/day), and ovx + GH (2.5 mg/kg/day) + PTH (80 microg/kg/day). After surgery, animals were left for 4 months to become osteopenic before the beginning of therapy. Hormone administrations were given 5 days per week for 2 months and the animals were killed. The L3 vertebra was removed and examined by pQCT densitometry and by histomorphometry. Compared with age-matched, sham-operated controls, there was a 21% decrease in total bone mineral content (BMC) (p < 0.0001), 17.0% decrease in total bone mineral density (BMD) (p < 0.0001), 25.4% decrease in cortical BMC (p < 0.001), 3.1% decrease in cortical BMD (p < 0.05), 50.5% decrease in cancellous BMC (p < 0.01), 47.3% decrease in cancellous BMD (p < 0.01), and 14.5% decrease in cancellous bone volume (BV/TV) (p < 0.05) in the vehicle-treated ovx rats. Compared with age-matched, vehicle-treated ovx controls, GH, PTH, and GH + PTH increased total BMC by 22.8% (p < 0.001), 32.4% (p < 0.0001), and 72.7% (p < 0.0001), respectively; total BMD by 9.7% (p > 0.05), 22.6% (p < 0.001), and 38.8% (p < 0.0001), respectively; cortical BMC by 28.8% (p < 0.01), 50.8% (p < 0.0001), and 98.4% (p < 0.0001), respectively; and cortical BMD by 4.5% (p < 0.01), 2.9% (p < 0.05), and 6.3% (p < 0.0001), respectively. PTH and GH + PTH significantly increased cancellous BMC by 95.3% (p < 0.01) and 255.8% (p < 0.0001), respectively; cancellous BMD by 77.6% (p < 0.05) and 181% (p < 0.0001), respectively; cancellous BV/TV by 38.6% (p < 0.0001) and 55.9% (p < 0.0001), respectively; and trabecular thickness by 48% (p < 0.0001) and 68.3% (p < 0.0001), respectively. Note that GH by itself had no significant effect on vertebral cancellous BMC, cancellous BMD, and cancellous BV/TV. In conclusion, the effect of PTH was mostly more marked than that of GH. GH acted mainly by increasing cortical bone with less effect on cancellous bone, while PTH acted by increasing both cortical and cancellous bones. Combined therapy with GH and PTH was more effective in rebuilding bone after ovariectomy than either therapy alone. The effects of combined therapy with GH and PTH were additive in vertebral bone in the aged osteopenic rats.     

Parathyroid hormone monotherapy and cotherapy with antiresorptive agents restore vertebral bone mass and strength in aged ovariectomized rats

Previous studies have shown that parathyroid hormone (PTH) monotherapy and cotherapy with estrogen or risedronate augment vertebral bone mass and bone strength in young, ovariectomized (OVX) rats. The current study was designed to determine whether PTH has similar bone anabolic effects in aged OVX rats at a much later stage of estrogen depletion. Female Sprague Dawley rats were subjected to sham surgery or bilateral ovariectomy at three months of age and maintained untreated for one year after surgery to allow for the development of vertebral osteopenia in OVX rats. Groups of baseline control and OVX rats were sacrificed at the end of this pretreatment period. The remaining OVX rats were then treated for ten weeks with vehicle, antiresorptive agents alone (estrogen, risedronate, or calcitonin), or PTH alone. Other groups of OVX rats were treated concurrently with PTH and each of the antiresorptive agents. The first and fourth lumbar vertebral bodies were processed undecalcified for quantitative bone histomorphometry and biomechanical testing, respectively. As expected, bone mass and compressive strength were decreased in the lumbar vertebral body of baseline OVX rats compared to baseline control rats. This bone loss was associated with decreases in trabecular number and width and an increase in trabecular separation. Treatment with estrogen, risedronate, or calcitonin alone failed to reverse the changes in bone mass, structure, and strength induced by ovariectomy. In contrast, treatment of OVX rats with PTH alone restored vertebral cancellous bone volume and ash density to the level of vehicle-treated control rats and increased vertebral maximum load, stress, and normalized load to well above this level. The hormone significantly increased trabecular width, but not number, in the lumbar vertebral body of OVX rats. Concurrent treatments with PTH and the antiresorptive agents did not augment cancellous bone and biomechanical competence to a greater, or lesser, extent than treatment with PTH alone. Compressive strength correlated significantly with bone mass and trabecular width in the lumbar vertebral body. These results indicate that PTH completely restores lost bone mass and improves bone strength in the vertebral body of aged OVX rats with established osteopenia. With our previous study in younger OVX rats, the current study demonstrates that the anabolic effect of PTH is independent of age and the stage of estrogen depletion in the rat skeleton.     

Increased trabecular bone mass in rats treated with human synthetic parathyroid hormone

Although PTH inhibits bone collagen synthesis acutely, prolonged administration of PTH increases trabecular bone mass. The objectives of this study were to develop a simple method to quantitate the anabolic response of cortical and trabecular bone, to determine if the trabecular bone response is at the expense of cortical bone, and to correlate the bone response with changes in serum calcium or phosphate. Subcutaneous injections of 2 to 16 μg/100 g body weight hPTH(1–34) were given daily to weanling rats for 12 days. The trabecular and cortical bone were manually separated from the distal femur, and calcium, hydroxyproline, and extracted dry weight were measured. Growth and renal function were not impaired. Serum calcium (range: 8.9–9.5 mg%) and serum phosphate (range: 7.7–8.5 mg%) did not differ significantly from control serum calcium, 9.1 mg%, or serum phosphate, 8.1 mg%. A dose-related anabolic response was observed in calcium, hydroxyproline, and dry weight of trabecular bone. At the highest dose of hPTH for 12 days, these values were increased above control by 26%, 33%, and 26%, respectively (P < .01). While cortical bone values increased over 12 days, only the dry weight increase was significant (P < .01). Our method showed an increase in trabecular bone mass after daily subcutaneous injections of hPTH (1–34) at doses that were neither toxic nor hypercalcemic. Although the absolute change of cortical bone mass was greater than that of trabecular bone, it was more variable and not statistically significant. Nevertheless, these results indicate that trabecular bone mass did not increase at the expense of cortical bone.     

Effects of parathyroid hormone alone or in combination with antiresorptive therapy on bone mineral density and fracture risk – a meta-analysis

Aim The effects of parathyroid hormone (PTH) alone or in combination with antiresorptive therapy on changes in bone mineral density (BMD) and fracture risk were studied. Materials and methods Randomised placebo controlled trials were retrieved from the PubMed, Web of Science or Embase databases. Results PTH alone or in combination with antiresorptive drugs reduced vertebral [relative risk (RR)=0.36, 95% confidence interval (CI): 0.28–0.47, 2p<0.01] and non-vertebral (RR=0.62, 95% CI: 0.48–0.82, 2p<0.01) fracture risk and increased spine BMD by 6.6% (95% CI: 5.2–8.1%, 2p<0.01) and hip BMD non-significantly by 1.0% (95% CI: −0.1 to 2.1%, 2p=0.08) during 11–36 months of follow-up (13 trials). The gain in spine and hip BMD tended to increase with the length of the PTH treatment. No significant effect of study duration on fracture risk could be demonstrated. The major adverse events were hypercalcaemia, nausea and discomfort at the injection sites. Only limited data are currently available on fracture risk reduction with PTH plus antiresorptive therapies. Conclusion Although the number of studies on non-vertebral fractures is limited, our pooled analysis revealed that PTH alone or in combination with antiresorptive drugs would appear to be able to reduce the risk of vertebral and non-vertebral fractures and to increase spine and perhaps hip BMD. However, these analyses were based on cross-sectional data – i.e. based on indirect comparisons – and further studies with a direct comparison of study duration are necessary. No studies comparing PTH, PTH plus antiresorptive drugs and antiresorptive drug versus placebo in a factorial design are available; consequently, we were unable to draw any conclusions on the superiority of PTH plus antiresorptive drug versus antiresorptive drug or PTH alone with respect to BMD or fractures.     

Human parathyroid hormone (1-34) increases mass and structure of the cortical shell,with resultant increase in lumbar bone strength,in ovariectomized rats

Estrogen deficiency causes reduction of bone mass and abnormal bone microarchitecture, consequently reducing bone strength. Human parathyroid hormone (hPTH) (1-34) increases bone mass and strength. To clarify the factors that determine the recovery of bone strength in the lumbar vertebrae of ovariectomized rats by intermittent hPTH administration, we analyzed the relationship between skeletal measurements and bone strength. Human PTH (1-34) administration resulted in recovery of cortical bone mineral content (BMC) and cortical bone area to sham the levels, but in resulted in a less pronounced recovery of trabecular BMC and no increase in the total cross-sectional area of the vertebral body. Of the three-dimensional (3D) trabecular bone parameters, hPTH (1-34) increased trabecular thickness (Tb.Th). The cortical shell area of L4, determined by histomorphometry, was also increased. In hPTH-treated rats, the only determinant of the compressive load of L5 was the cortical shell BMC, in the early recovery period (days 42–84). Our data suggest that increased cortical bone mass contributes more than trabecular bone mass and structure to the recovery of bone strength in response to hPTH therapy in the rat lumbar vertebral body after ovariectomy.     

Skeletal effects of parathyroid hormone infusion in ovariectomized rats with or without estrogen repletion.

We employed skeletally matured rats to study changes in biochemical markers of bone turnover, bone mineral density (BMD), and bone biomechanics produced by continuous elevation of parathyroid hormone (PTH) in estrogen-deplete and -replete rodents. Ninety-six 7-month-old virgin female rats were divided randomly into 12 groups (n = 8) and treated as follows. One group was killed on the day of surgery. The remaining groups were either bilaterally ovariectomized (Ovx) or sham-operated and left untreated for 8 weeks, at which point, two groups, one sham and one Ovx, were killed. The remaining nine groups were treated for 2 weeks or 4 weeks. One sham and two Ovx groups received subcutaneous implants of Alzet miniosmotic pumps with vehicle for PTH. Two Ovx groups were given pumps with vehicle as well as a subcutaneous implant of 17beta-estradiol, which delivered 10 microg/kg per day. Two Ovx groups were implanted with rat PTH(1-34) in Alzet miniosmotic pumps, which delivered 30 microg PTH/kg per day. Two Ovx groups were implanted with both estradiol pellets and PTH-loaded pumps. One group of Ovx animals from each treatment was killed after 2 weeks and the other after 4 weeks. Biochemical markers of bone turnover, serum osteocalcin and urinary free pyridinoline, BMD, and mechanical strength of excised bones were measured. As expected, there was a significant increase in N-terminal PTH and serum calcium levels in all PTH infusion groups. Both serum osteocalcin and urinary pyridinoline showed a rapid increase within the first 2 weeks of the PTH infusion and remained elevated at week 4. In estrogen-replete groups, osteocalcin increased by week 2 of PTH infusion but pyridinoline did not increase until week 4. BMD of the distal and proximal femur showed the expected decrease 8 weeks after ovariectomy but did not exhibit any further changes during the 4 weeks of treatment with vehicle. Four weeks of PTH infusion in Ovx animals resulted in BMD loss at the midshaft, distal, and proximal regions of the femur. Estrogen repletion by itself, beginning 8 weeks after ovariectomy, produced no change in BMD at any site when compared with from Ovx vehicle-treated rats. Estrogen repletion in PTH-infused Ovx animals resulted in significant improvements of BMD comparable with sham-operated animals at all three femoral regions. The indentation test at the cancellous bone of the distal femur, three-point bending test at the midshaft femur, and cantilever bending test at the femoral neck showed that the changes in mechanical strength in these sites were consistent to the changes found in BMD. Our results showed that (1) continuously elevated levels of PTH induced additional loss of BMD in estrogen-deficient animals beyond the rapid bone loss phase associated with ovariectomy, (2) estrogen repletion, given by implant, to PTH-infused Ovx animals, reversed these BMD changes increasing BMD to levels comparable with estrogen-sufficient rats, and (3) these changes were reflected in the mechanical strength determined at these sites. These results lend experimental support that hormone replacement therapy may benefit bone health in postmenopausal women with primary hyperparathyroidism (PHPT). In addition, it raises the possibility that a continuous elevation of PTH could exert anabolic effects on skeletal tissue if its catabolic component can be minimized.     

雌激素调节一氧化氮的骨形成增加作用

[目的]探讨雌激素对卵巢切除大鼠血浆硝酸盐／亚硝酸盐水平的影响。[方法]通过免疫组织化学染色法检测一氧化氮合成酶在骨组织中的表达，双能X射线测定骨矿密度值，图像分析系统进行骨形态学计量学测量，光密度法测定血浆硝酸盐／亚硝酸盐水平。[结果]卵巢切除导致血浆硝酸盐／亚硝酸盐水平及骨矿密度值、小梁骨体积等骨形态学计量学参数显著下降，雌激素抑制了卵巢切除导致的这些变化。一氧化氮合成酶免疫活性信号在成骨细胞内测得，雌激素组一氧化氮合成酶信号较卵巢切除组显著性增强。[结论]雌激素通过诱导一氧化氮的产生而刺激骨形成，一氧化氮是雌激素诱导骨形成增加的介导剂。     

The influence of combined parathyroid hormone and growth hormone treatment on cortical bone in aged ovariectomized rats.

The influence of combined parathyroid hormone (PTH) and growth hormone (GH) treatment on bone formation and mechanical strength was investigated in femoral middiaphysial cortical bone from 20-month-old ovariectomized (OVX) rats. The animals were OVX at 10 months of age, and at 18 months they were treated daily for 56 days with PTH(1-34) alone (60 microg/kg), recombinant human GH (rhGH) alone (2.7 mg/kg), or a combination of PTH(1-34) plus rhGH. Vehicle was given to OVX control rats. All animals were labeled at day 28 (calcein) and at day 49 (tetracycline) of the treatment period. PTH(1-34) alone gave rise to formation of a new zone of bone at the endocortical surface. rhGH alone caused substantial bone deposition at the periosteal surface without influencing the endocortical surface. Combined PTH(1-34) plus rhGH administration enhanced bone deposition at the periosteal surface to the same extent as that of rhGH alone. However, the combined treatment resulted in a more pronounced formation of new bone at the endocortical surface than was induced by PTH(1-34) alone. Both PTH(1-34) alone and rhGH alone increased the mechanical strength of the femoral diaphysis, and further increase in mechanical strength resulted from combined PTH(1-34) plus rhGH treatment. OVX by itself induced the characteristic increase in medullary cavity cross-sectional area and a minor decrease in the mechanical quality of the osseous tissue.     

Daily transient decreases in plasma parathyroid hormone levels induced by the calcimimetic NPS R-568 slows the rate of bone loss but does not increase bone mass in ovariectomized rats

Daily parathyroid hormone (PTH) injections that transiently increase plasma PTH levels within the physiological range increase bone mass in osteopenic, ovariectomized (ovx) rats. This study tested the hypothesis that repeated transient decreases in plasma PTH levels from normal, induced by the daily oral administration of the calcimimetic NPS R-568, would induce an anabolic effect in bone of ovx rats with established osteopenia and/or prevent the rapid bone loss that occurs following ovx. In the reversal study, NPS R-568 was administered orally (10 or 100 micromol/kg) for 30 days to 14-month-old retired breeder rats that were ovx 5 months earlier. NPS R-568 treatment did not increase bone formation rate (BFR) or cancellous bone area (B.Ar) in the proximal tibial metaphysis, or bone mineral density (BMD), at any femoral site. In the prevention study, 3-month-old virgin rats were ovx and given NPS R-568 for the following 28 days. The 10 micromol/kg dose prevented the increase in osteoclast number and 42% of the loss of B.Ar, without affecting the elevated osteoblast populations or BFR. Surprisingly, the 100 micromol/kg dose had fewer protective effects, despite preventing the increase in BFR in both cancellous and cortical bone. Detailed analysis of cancellous bone showed that tendency for a dose-related protection of true cancellous bone occurred, but, while the 10 micromol/kg dose prevented 88% of the loss of calcified cartilage seen in control ovx rats, the 100 micromol/kg dose increased that loss by a further 31%. The mechanism underlying these disparate effects of NPS R-568 on calcified cartilage accumulation in the tibial metaphysis is unclear, but may be related to the different effects that the two doses have on plasma Ca(2+) levels. In conclusion, transient increases in PTH levels above basal, and not simple oscillations in hormone levels below normal, appear necessary for the anabolic properties of endogenous PTH to be manifested in the bones of osteopenic ovx rats.     

Effect of parathyroid hormone (hPTH[1-84]) treatment on bone mass and strength in ovariectomized rats.

Skeletal fragility in osteoporotic patients is a prominent underlying cause of low-trauma fractures of most bone sites in humans. Clinical research is now focused on developing treatment strategies, including anabolic agents such as parathyroid hormone (PTH), to recover osteoporosis-related bone loss. Female Sprague-Dawley rats (4.5 mo old) were allowed to become osteopenic for 10 wk postovariectomy. Eight rats were killed at the time of ovariectomy (-10 wk) as a baseline control; sham and ovariectomized (OVX) groups were killed at wk 0. Eight rats per group (sham, OVX + vehicle, OVX + hPTH [5 d/wk], and OVX + hPTH [3 d/wk]) were killed after 4, 8, 14, and 20 wk of treatment with 50 microg/kg of human parathyroid hormone (hPTH[1-84]). Bone mineral content and density were measured only in the vertebral body. Bone strength was evaluated in the vertebral body, femoral diaphysis, femoral neck, and distal femur. Significant, lasting osteopenia developed in the vertebral body of OVX rats by 10 wk postovariectomy. Bone mineral density of the vertebral body partially recovered by 8 wk and fully recovered to that seen in sham animals only by 20 wk posttreatment with either a 5 or 3 d/wk dosing schedule of PTH[1-84]. Therefore, hPTH[1-84] (50 microg/kg) given either 3 or 5 d/wk fully restores vertebral and femoral bone strength in osteopenic OVX rats.     

卵巢切除大鼠血清甲状旁腺素、降钙素变化与骨质量降低

本以OVX大鼠为动物模型，观察了去势15天、30天和60天大鼠血清甲状旁腺激素(PTH)和降钙素(CT)含量，第6胸椎(T6)，第3腰椎(L3)和股骨矿盐含量及骨力学参数的变化。实验结果表明，去势15天、30天和60天大鼠血清CT显降低，去势30天和60天大鼠血清PTH显降低。去势15天大鼠T6横截面积显降低，去势60天大鼠T6类骨质含量显增加。去势15天和30天大鼠L3矿盐含量显降低，30天骨压缩强度显降低，60天最大应力、杨氏模量显降低，横截面积显增加。去势15天和3D天大鼠股骨弯曲应力、张应力显降低，弹性能密度在30天显降低，去势60天股骨近l／3部位矿盐含量显降低。实验结景提示．()VX大鼠CT降低是引起骨质丢失、骨力学性能低下的一个重要因素。松质骨骨丢失早于皮质骨．但力学性能的降低晚于皮质骨，()Vx大鼠骨有机质减少是非腔原蛋白减少。     

Maintenance of increased bone mass after recombinant human parathyroid hormone (1-84) with sequential zoledronate treatment in ovariectomized rats.

The concept of lose, restore, maintain (LRM) for reversing existing osteoporosis was tested in rats. The withdrawal of PTH results in the loss of the acquired bone mass, but sequential therapy with zoledronate quite effectively maintained the PTH(1-84)-acquired bone quantity and quality. INTRODUCTION: Because antiresorptive agents against osteoporosis are presently quite limited, strong anabolic agents such as human parathyroid hormone (hPTH) are quite helpful. However, because hPTH(1-34) is available only through injection and has a critical side effect of causing bone tumors during life-long administration in the rat, it would be practical to use PTH for the shortest possible duration to obtain the maximal effect. To determine the effectiveness of the osteoporosis-reversing concept of lose, restore, and maintain (LRM), recombinant hPTH(1-84) [rhPTH(1-84)] and the respective antiresorptive agents were sequentially studied. MATERIALS AND METHODS: Thirty-six, 20-week-old Sprague-Dawley rats were used. Treatment started at the 25th week after ovariectomy, which was performed at 20 weeks of age, with 5 weeks of rhPTH(1-84) 100 microg/kg/day, 5 days/week, followed by the respective sequential therapies for 5 weeks as follows: (1) ovariectomized rats (OVX; n = 6), (2) sham-operated rats (SHAM; n = 6), (3) OVX rats with PTH maintenance (PTH-M; n = 6), (4) OVX rats treated with PTH and then PTH was withdrawn (PTH-W; n = 6), (5) PTH-treated OVX rats treated with 17beta-estradiol (PTH-E; 10 microg/day SC, 5 days/week; n = 6), and (6) PTH-treated OVX rats treated with zoledronate (PTH-Z; 12.5 microg/kg SC weekly; n = 6). BMD of the right femora was measured by DXA. microCT was used to measure the structural parameters of the second lumbar vertebrae. Three-point bending test of the femora and compressive tests of vertebrae were also performed. RESULTS: Bone quantity data showed that the BMD and most of the microstructural parameters were significantly higher in the PTH-M and PTH-Z groups than in the OVX and PTH-W groups (p < 0.05). Measurement of the cortical thickness revealed that only the PTH-M group showed a significant increase (p = 0.001). The ultimate force (Fu) at the midshaft of the femora was similar in the treated groups and stronger than in the OVX group (p < 0.05). However, in the vertebrae, the Fu of the PTH-M and PTH-Z groups was significantly higher, by approximately 44-47%, than in the OVX and PTH-E groups and showed a higher tendency than in the PTH-W group. CONCLUSION: PTH withdrawal resulted in the loss of acquired BMD, and sequential therapy with antiresorptives prevented further loss (17beta-estradiol versus zoledronate). The zoledronate after rhPTH(1-84) as a sequential regimen was quite consistently effective.     

Calcimimetics maintain bone turnover in uremic rats despite the concomitant decrease in parathyroid hormone concentration

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Maintenance of cortical bone in human parathyroid hormone(1-84)-treated ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone(1-84) (hPTH) followed by maintenance treatment with 17beta-estradiol (E(2)), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on cortical bone in the ovariectomized (ovx) rat. Eight groups of ovx and one group of intact female rats (3.5 months) were left untreated for 11 weeks. For the following 12 weeks, four groups received subcutaneous injections of hPTH (75 microg/kg per day on 3 days/week) and four groups received vehicle. Treatments were then changed to E(2) (10 microg/kg per day on 2 days/week), Ris (3 microg/kg per day on 3 days/week), LowPTH (25 microg/kg per day on 3 days/week), or vehicle. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). Bone mineral density (BMD) and bone mineral content (BMC) of the diaphyseal femur and total cross-sectional area (Tt.Ar), marrow area (Ma.Ar), cortical area (Ct.Ar), and periosteal and endocortical bone formation of the tibia were measured. Ovariectomy resulted in lower BMD (weeks 0-48), unaffected BMC, and greater Tt.Ar (weeks 12 and 36), Ma.Ar (week 48), and Ct.Ar (weeks 0 and 12) compared with intact rats. Endocortical and periosteal bone formation were greater in the ovx than in the intact rats up to 23 weeks postovariectomy. Treatment of ovx rats with hPTH for 12 weeks resulted in greater cortical BMD, BMC, and endocortical bone formation than in intact or ovx controls. In ovx rats pretreated with hPTH and then treated with Ris for 36 weeks, BMD and BMC were greater and Ma.Ar was smaller than in ovx controls. In ovx rats pretreated with hPTH and then treated with LowPTH, BMD, BMC, Ct.Ar, and endocortical bone formation were greater and Ma.Ar was smaller than in ovx controls. Treatment of hPTH-pretreated rats with E(2) for 36 weeks did not affect cortical BMD, BMC, and Ct.Ar, although periosteal bone formation was lower in the E(2) group compared with the ovx group. Thus, in ovariectomized rats, cortical bone gained by 12 weeks of hPTH treatment was maintained for up to 36 weeks by treatment with risedronate or low-dose hPTH, but not with 17beta-estradiol.     

Sequential treatment with basic fibroblast growth factor and parathyroid hormone restores lost cancellous bone mass and strength in the proximal tibia of aged ovariectomized rats.

This study was designed to determine whether sequential treatment with basic fibroblast growth factor (bFGF) and parathyroid hormone (PTH) can restore lost cancellous bone mass and strength at a severely osteopenic skeletal site in aged ovariectomized (OVX) rats. Female Sprague-Dawley rats were subjected to sham surgery or ovariectomy at 3 months of age and maintained untreated for the first year after surgery. At 15 months of age, groups of baseline control and OVX rats were killed and catheters were inserted in the jugular veins of all remaining rats. Two groups of OVX rats were injected intravenously (iv) daily with bFGF for 14 days at a dose of 200 microg/kg body weight. At the end of bFGF treatment, one group was killed whereas the other group was subjected to 8 weeks of treatment with synthetic human PTH 1-34 [hPTH(1-34)] consisting of subcutaneous (sc) injections 5 days/week at a dose of 80 microg/kg. Another group of OVX rats was treated iv with vehicle for 2 weeks followed by treatment with PTH alone for 8 weeks. Other groups of sham-operated control rats and OVX rats were treated iv and sc with vehicle alone. The right proximal tibia from each rat was processed undecalcified for quantitative bone histomorphometry and the left proximal tibia was subjected to biomechanical testing. Baseline and vehicle-treated OVX rats were severely osteopenic because their tibial cancellous bone volumes were less than 5% compared with mean values of 20.3% and 15.0% in baseline and vehicle-treated control rats, respectively. Treatment of OVX rats for 2 weeks with bFGF alone did not significantly increase tibial cancellous bone volume but induced marked increases in osteoid volume, osteoblast surface, and osteoid surface. Sequential treatment of aged OVX rats with bFGF and PTH increased tibial cancellous bone volume (15.1%) and load to failure to at least the level of vehicle-treated control rats. Tibial cancellous bone volume (10.8%) and load to failure also were significantly increased by treatment with PTH alone, and these variables were not significantly different from those of OVX rats treated with bFGF + PTH. However, tibial ash density was significantly greater in OVX rats treated sequentially with bFGF and PTH compared with OVX rats treated with PTH alone. Our findings suggest that sequential treatment with bFGF and PTH may be useful for restoration of lost cancellous bone in the severely osteopenic, estrogen-deplete skeleton, but it cannot be concluded with certainty that this sequential treatment has a greater bone restorative effect than treatment with PTH alone.     

Parathyroid hormone added to established hormone therapy: effects on vertebral fracture and maintenance of bone mass after parathyroid hormone withdrawal.

Our best pharmacologic agents for osteoporosis treatment prevent no more than 40-60% of osteoporotic fractures in patients at highest risk. Thus, there is a need for agents that can further augment bone mass and reduce fracture risk more substantially. To this end, we investigated the utility of parathyroid hormone (PTH) in combination with established hormone-replacement therapy (HRT) in women with osteoporosis. Fifty-two women who had been on HRT for at least 2 years were enrolled in this trial in which 25 were assigned randomly to remain on HRT alone and 27 were assigned to remain on HRT and also receive daily subcutaneous PTH(1-34) 400 U (25 microg) per day for 3 years. Bone mineral density (BMD) measurements at the spine, hip, and total body as well as biochemical determinations of bone turnover and calcium homeostasis were obtained every 6 months. Lateral thoracic and lumbar spine X-rays were obtained at baseline and annually. Subjects also had measurements of bone density and biochemical indices of bone turnover 1 year after discontinuation of PTH, while HRT was continued. In the group receiving HRT alone, bone density and biochemical variables of bone turnover remained stable throughout the 3-year treatment trial and 1-year follow-up. In the PTH + HRT group, biochemical variables of bone formation and resorption peaked at 6 months and subsequently remained elevated until 30 months at which time levels were indistinguishable from baseline. Subjects in the PTH + HRT group increased bone mass by 13.4+/-1.4% in the spine, 4.4+/-1.0% in the total hip, and 3.7+/-1.4% in the total body. Bone density measurements remained stable 1 year after discontinuation of PTH without any significant loss while women continued HRT. Biochemical variables did not change significantly after cessation of PTH through the 1-year follow-up period. PTH + HRT reduced the percent of women who had vertebral fractures from 37.5% to 8.3% (using a 15% height reduction criterion) and from 25% to 0% (using a 20% height reduction criterion) compared with women receiving HRT alone (p < 0.02 for both). We conclude that ongoing HRT maintains almost all of the PTH-induced bone mass increment for 1 year after discontinuation of PTH. Furthermore, PTH in combination with hormone therapy is an effective means of increasing bone mass throughout the skeleton and specifically reducing vertebral fracture occurrence by 75-100%, compared with HRT alone.     

Minocycline prevents the decrease in bone mineral density and trabecular bone in ovariectomized aged rats

In the current study, we examined the effects of minocycline, on the osteopenia of ovariectomized aged rats. Old female rats were randomly divided into five groups: sham, ovariectomized control and ovariectomized treated with minocycline, 17β-estradiol, or both agents. Bone samples were collected 8 wk after the treatment. Ovariectomy reduced bone mineral density of the whole femur and at the condylar, distal metaphyseal and head-neck-trochanter regions 10%–19% and the loss of bone density was prevented by treatment with minocycline or 17β-estradiol. Histomorphometric analysis of distal femur showed ovariectomy reduced the trabecular bone area, the trabecular bone number, trabecular bone thickness and increased the trabecular bone separation. The microanatomic structure of trabecular bone also showed that the number of nodes, node to node, cortical to node, node to free end was reduced by ovariectomy. Treatment with minocycline attenuated the effect of ovariectomy on trabecular bone in aged animals. In contrast, cortical bone was not affected by ovariectomy or minocycline treatment. The effect of minocycline on bone turnover was also examined. Minocycline increased osteoid surface, mineralizing surface, mineral apposition rate, bone formation rate and reduced eroded surface. We have therefore concluded that the modest increase in bone mineral density and the improvement in the trabecular bone status noted in minocycline treated ovariectomized aged rats is likely due to an increase in bone formation coupled with a decrease in bone resorption.     

Effect of alendronate and intermittent parathyroid hormone on implant fixation in ovariectomized rats

Background  Intermittent administration of parathyroid hormone (PTH) leads to bone formation by increasing osteoblast numbers and activity levels. Animal studies have shown that intermittent PTH administration increases implant fixation in normal rats. The purpose of this study was to analyze the osseous incorporation of an implant in osteoporotic rats while treating them with intermittent PTH (1–34) or alendronate. Methods  A total of 36 ovariectomized (OVX) Wistar rats were randomized into three groups. Polymethylmethacrylate cement rods were implanted in one tibia in each rat. The three groups received daily PTH (60 μg/kg body weight [BW]), alendronate (200 μg/kg BW), or saline (0.5 ml/kg BW). A sham-ovariectomized group (n = 12) was treated with saline. After 2 weeks, the area around the implants was analyzed by histomorphometry for bone volume density (BVD) and implant bone contact. Bone mineral density (BMD) was evaluated by dual-energy X-ray absorptiometry. Results  The BVD was higher in the specimens treated with PTH than in the other groups. PTH improved the BVD, BMD, and implant bone contact. Alendronate doubled the implant bone contact compared to the OVX and sham groups but did not improve BVD or BMD. Conclusions  These findings confirm that intermittent PTH enhances implant fixation in osteoporotic bone. The clinical significance of these findings is that application of intermittent PTH may be beneficial for early implant fixation in fractures, nonunions, and prosthetic replacements when bone density is decreased.