Osteopenic Rat Model Research Articles

Wnt16 Increases Bone-to-Implant Contact in an Osteopenic Rat Model by Increasing Proliferation and Regulating the Differentiation of Bone Marrow Stromal Cells

Osseointegration is a complex biological cascade that regulates bone regeneration after implant placement. Implants possessing complex multiscale surface topographies augment this regenerative process through the regulation of bone marrow stromal cells (MSCs) that are in contact with the implant surface. One pathway regulating osteoblastic differentiation is Wnt signaling, and upregulation of non-canonical Wnts increases differentiation of MSCs on these titanium substrates. Wnt16 is a non-canonical Wnt shown to regulate bone morphology in mouse models. This study evaluated the role of Wnt16 during surface-mediated osteoblastic differentiation of MSCs in vitro and osseointegration in vivo. MSCs were cultured on Ti substrates with different surface properties and non-canonical Wnt expression was determined. Subsequently, MSCs were cultured on Ti substrates +/−Wnt16 (100 ng/mL) and anti-Wnt16 antibodies (2 μg/mL). Wnt16 expression was increased in cells grown on microrough surfaces that were processed to be hydrophilic and have nanoscale roughness. However, treatment MSCs on these surfaces with exogenous rhWnt16b increased total DNA content and osteoprotegerin production, but reduced osteoblastic differentiation and production of local factors necessary for osteogenesis. Addition of anti-Wnt16 antibodies blocked the inhibitor effects of Wnt16. The response to Wnt16 was likely independent of other osteogenic pathways like Wnt11-Wnt5a signaling and semaphorin 3a signaling. We used an established rat model of cortical and trabecular femoral bone impairment following botox injections (2 injections of 8 units/leg each, starting and maintenance doses) to assess Wnt16 effects on whole bone morphology and implant osseointegration. Wnt16 injections did not alter whole bone morphology significantly (BV/TV, cortical thickness, restoration of trabecular bone) but were effective at increasing cortical bone-to-implant contact during impaired osseointegration in the botox model. The mechanical quality of the increased bone was not sufficient to rescue the deleterious effects of botox. Clinically, these results are important to understand the interaction of cortical and trabecular bone during implant integration. They suggest a role for Wnt16 in modulating bone remodeling by reducing osteoclastic activity. Targeted strategies to temporally regulate Wnt16 after implant placement could be used to improve osseointegration by increasing the net pool of osteoprogenitor cells.

Could fructan sources in strawberry matrix be more effective as a tool for improvement of bone structure than these compounds added to diet alone? - Study on osteopenic rat model.

Osteoporosis, a disease associated with ovarian hormone deficiency following menopause, is the most common cause of age-related bone loss. Although an optimal intake of Ca is vital - both bone accretion during growth and maintenance in adult life - a great percentage of the population consumes far below the recommended amounts of this mineral. On the other hand, there are evidences that fructans enhance not only Ca absorption, but bone calcium as well. In the knowledge that estrogen deficiency and insufficient Ca in the diet during postmenopause cause serious problems with resultant osteoporosis, the aim of this study is to assess the effects of a diet enriched in fructan-containing sources alone, or in the "strawberry matrix", on the structure of bone in OVX rats under calcium hypoalimentation. Experimental animals were female Wistar rats, sham-operated or ovariectomized. The treatment with Ca-restricted diets also contained one of the sources of fructan (Jerusalem artichoke, yacon, Beneo Orafti Synergy1), in the amount providing 8% of fructans. Femur architecture of rats was assessed by tomography and Ca content by the AAS method. Ovariectomy led to a significant decrease in femoral Ca content, total mineral content and bone density of rats. This study shows that a diet containing inulin-type fructan (especially as a component of strawberry product) improved bone quality (i.e. increase in Ca content in femur, total density in middle part of bone, as well as decrease of endosteal circumference) in OVX rats under calcium hypoalimentation. These findings suggest that a fructan-enriched diet could be potentially useful for postmenopausal osteoporosis. It is important to determine an optimal dietary level of fructan with the long-term goal of developing a dietary strategy in osteoporosis prevention.

Vitamin C reverses bone loss in an osteopenic rat model of osteoporosis.

Fruits and vegetables are rich in vitamin C with antioxidant properties which are known to influence bone quality. This study evaluated whether vitamin C (1000 mg/L) added to drinking water reverses the bone loss in ovariectomized rats. Ninety-day-old female Sprague-Dawley rats were randomly assigned to either sham (n = 14) or ovariecotmized groups (n = 28). Sixty days after ovariectomy, the treatments were sham, ovariectomy (OVX), OVX + vitamin C (22 mg oral intake daily) for 60 days. Urine was collected for deoxypyridinoline (DPD) evaluation, rats were sacrificed, and antioxidant capacity, osteopontin, alkaline phosphatase (ALP), and bone specific tartrate resistant acid phosphatase (TRAP) were evaluated in the plasma. Right femur and 5th lumbar were evaluated for bone density, strength, ash, Ca, and Mg concentrations. Antioxidant capacity, ALP activity, osteopontin decreased (p-value < 0.05), while TRAP and urinary DPD increased (p-value < 0.05) with ovariectomy. In contrast, vitamin C increased (p-value < 0.05) antioxidant capacity, ALP activity, osteopontin concentration and reduced (p-value < 0.05) TRAP and urinary DPD excretion, respectively. Ovariectomy reduced (p-value < 0.05) bone quality, bone ash, Ca and Mg concentrations. Vitamin C increased (p-value < 0.05) femoral density without affecting (p-value > 0.1) femoral strength, ash, or Ca, and Mg concentrations, while it increased (p-value < 0.05) the 5th lumbar density, ash, and Ca and Mg concentrations. In conclusion, vitamin C increased bone quality and antioxidant capacity in ovariectomized rats.

The Effect of Vibration Treatments Combined with Teriparatide or Strontium Ranelate on Bone Healing and Muscle in Ovariectomized Rats.

The aim of the present study was to study the effect of combined therapy of teriparatide (PTH) or strontium ranelate (SR) with whole-body vibration (WBV) on bone healing and muscle properties in an osteopenic rat model. Seventy-two rats (3months old) were bilaterally ovariectomized (Ovx), and 12 rats were left intact (Non-Ovx). After 8weeks, bilateral transverse osteotomy was performed at the tibia metaphysis in all rats. Thereafter, Ovx rats were divided into six groups (n=12): (1) Ovx-no treatment, (2) Ovx+vibration (Vib), (3) SR, (4) SR+Vib, (5) PTH, and (6) PTH+Vib. PTH (40μg/kg BW sc. 5×/week) and SR (613mg/kg BW in food daily) were applied on the day of ovariectomy, vibration treatments 5days later (vertical, 70Hz, 0.5mm, 2×/day for 15min) for up to 6weeks. In the WBV+SR group, the callus density, trabecular number, and Alp and Oc gene expression were decreased compared to SR alone. In the WBV+PTH group, the cortical and callus widths, biomechanical properties, Opg gene expression, and Opg/Rankl ratio were increased; the cortical and callus densities were decreased compared to PTH alone. A case of non-bridging was found in both vibrated groups. Vibration alone did not change the bone parameters; PTH possessed a stronger effect than SR therapy. In muscles, combined therapies improved the fiber size of Ovx rats. WBV could be applied alone or in combination with anti-osteoporosis drug therapy to improve muscle tissue. However, in patients with fractures, anti-osteoporosis treatments and the application of vibration could have an adverse effect on bone healing.

Imbalanced Diet Deficient in Calcium and Vitamin D- Induced Juvenile Osteopenia in Rats; the Potential Therapeutic Effect of Egyptian Moghat Roots Water Extract (Glossostemon bruguieri).

This study aimed to explore and validate a new juvenile osteopenic (JO) rat model then examine the efficacy of moghat (Glossostemon bruguieri) as an alternative reversal therapy for JO. Phytochemical screening analysis showed that moghat contains 5.8% alkaloids, 1.5% flavonoids and 13.2% total phenols. Juvenile osteopenia was induced in 15 days old Sprague- Dawley female rats by feeding them free Ca and vitamin D synthetic diet for 21 days. Osteopenic rats were either treated with moghat (0.8 g dried plant tissue/Kg body weight, orally), or with a reference nutritional supplements of calcium chloride (14 mg Ca/Kg) and vitamin D3 (7 IU/Kg), for extra 21 days. Both untreated and treated groups were compared to a control group that fed a regular pelleted food. Our results showed that osteopenic rats lost normal bone tissue architecture, 30 % of body mass, 54 % of bone mass and finally 93% of bone calcium mass. Furthermore, these rats showed a markedly increase in serum phosphate, PTH, alkaline phosphatase, aspartate transaminase activities and creatinine level as compared to the control group. Moghat administration was successfully reversed osteopenia by normalizing body and bone masses to the reference ranges, increased the bone calcium mass by 17 fold without any detectable side effects on liver and kidney physiological performance. Therefore, moghat could be considered as potent safe -JO- reversal extract.

Is decreased bone mineral density associated with development of scoliosis? A bipedal osteopenic rat model

BackgroundAn association between adolescent idiopathic scoliosis and osteopenia has been proposed to exist. It is still not clear whether there is such an association and if so, whether osteopenia is a causative factor or a consequence. Our previous pilot studies have suggested the presence of osteopenia in scoliotic animals. The aim of this study was to investigate the development of scoliosis in an unpinealectomized bipedal osteopenic rat model, implementing osteoporosis as a causative factor.MethodsFifty Sprague-Dawley rats were rendered bipedal at the 3rd postnatal week and separated into control (25 rats) and heparin (25 rats receiving 1 IU/gr body weight/day) groups. DEXA scans after 4 weeks of heparin administration showed low bone mass in the heparin group. Anteroposterior and lateral x-rays of the surviving 42 animals (19 in heparin and 23 in control groups) were taken under anesthesia at the 40th week to evaluate for spinal deformity. Additional histomorphometric analysis was done on spine specimens to confirm the low bone mass in heparin receiving animals. Results of the DEXA scans, histomorphometric analysis and radiological data were compared between the groups.ResultsBone mineral densities of rats in the heparin group were significantly lower than the control group as evidenced by both the DEXA scans and histomorphometric analyses. However, the incidence of scoliosis (82% in heparin and 65% in control; p > 0.05) as well as the curve magnitudes (12.1 ± 3.8 in heparin versus 10.1 ± 4.3 degrees in control; p > 0.05) were not significantly different. Osteopenic rats were significantly less kyphotic compared to control specimens (p = 0.001).ConclusionsThis study has revealed two important findings. One is that bipedality (in the absence of pinealectomy) by itself may be a cause of scoliosis in this animal model. Further studies on animal models need to consider bipedality as an independent factor. Secondly, relative hypokyphosis in osteopenic animals may have important implications. The absence of sagittal plane analyses in previous studies makes comparison impossible, but nonetheless these findings suggest that osteopenia may be important in the development of 3D deformity in adolescent idiopathic scoliosis.

Bone Mineral Density Changes after Ovariectomy in Rats as an Osteopenic Model : Stepwise Description of Double Dorso-Lateral Approach

This study describes a method for inducing osteopenia using bilateral ovariectomy (OVX), which causes significant changes in bone mineral density (BMD) in rats. Twenty-five 10-week-old female Sprague Dawley rats were used. Five rats were euthanized after two weeks, and BMD was measured in their femora. The other 20 rats were assigned to one of two groups : a sham group (n = 10), which underwent a sham operation, and an OVX group (n = 10), which underwent bilateral OVX at 12 weeks of age. After six weeks, five rats from each group were euthanized, and BMD was measured in their femora. The same procedures were performed in the remaining rats form each group eight weeks later. The femur BMD was significantly lower in the six-week OVX group than in the six-week sham group, and in the eight-week OVX group than in the eight-week sham group. Bilateral OVX is a safe method for creating an osteopenic rat model. The significant decrease in BMD appears six weeks after bilateral OVX.

Protective effects of amlodipine and lacidipine on ovariectomy-induced bone loss in rats

Bone is a dynamic organ system that is directly related to calcium and phosphor metabolism. Imbalance in these two parameters upon aging or menopause leads to osteoporosis. Recently, it was also shown by researchers that high blood pressure in elderly women is statistically associated with decreased bone mineral content at the femoral neck, which may increase the susceptibility to fractures. The aim of our study was to investigate the effects of different doses of amlodipine and lacidipine on ovariectomized rat femurs' calcium and phosphor content. Bone calcium and phosphor concentration was measured by a Wavelength Dispersive Spectrometer. Calcium contents of the rat femurs were significantly lower in the ovariectomized group than in the sham group eight weeks after the operation. Amlodipine treatment at doses of 1 and 3 mg/kg significantly increased the calcium ( P < 0.01) and phosphor concentrations ( P < 0.01) in the femurs of ovariectomized rats, compared to those of control (ovariectomized) group. Both doses of lacidipine (1 and 3 mg/kg) also effectively increased calcium concentrations ( P < 0.01) significantly in ovariectomized rats. On the other hand amlodipine treatment at doses of 1 and 3 mg/kg significantly increased the calcium ( P < 0.01) and phosphor concentrations ( P < 0.01) in the femurs of ovariectomized rats compared with those of the sham group. In conclusion, amlodipine and lacidipine improved the bone loss in an ovariectomy induced osteopenic rat model. Our findings suggest that potent calcium channel blockers such as amlodipine and lacidipine have a beneficial effect on bone metabolism, and an antihypertensive effect.

Disuse and orchidectomy have additional effects on bone loss in the aged male rat

A severely osteopenic rat model was obtained by combining orchidectomy (ORX) and disuse (due to local paralysis induced by botulinum toxin [BTX] in the quadriceps muscle). Forty-two aged male rats (5-6 months old) were randomized into three groups: 18 were SHAM operated; 6 were ORX; and 18 were ORX and BTX injected in the right hindlimb. One, two, and three months after surgery, bone mass (BV/TV) and microarchitectural parameters (Tb.Th, Tb.N, Tb.Sp, Tb.Pf, and structure model index [SMI]) were measured by microcomputed tomography (microCT) on the primary and secondary spongiosa of the femur. Osteoid parameters (OS/BS, O.Th), the number of osteoclasts (Nb.Oc), and the mineral apposition rate (Ct.MAR, Cn.MAR) were measured by histology. The serum tartrate-resistant acid phosphatase (TRAcP) 5b activity was measured by immunoassay. ORX induced a decrease of BV/TV, Tb.N and an increase of Tb.Sp, Tb.Pf, and SMI on both primary and secondary spongiosa. ORX and BTX had cumulative effects on bone loss, since differences were maximized on the right femur. The decrease in BV/TV reached -65%. Osteoid parameters and mineral apposition rate increased during the time course of the study. A peak of serum TRAcP was found at 7 days post-ORX. TRAcP levels reached the highest values in the ORX-BTX groups and the effect lasted longer than in the group with ORX alone. The association of ORX-BTX induced a greater bone resorption, due to the removal of complete trabeculae, compared to ORX alone. This model induced a severe and rapid bone loss and can be used to explore pharmacological- and biomaterial-based countermeasures.

Evaluation of an injectable bone substitute (βTCP/hydroxyapatite/hydroxy‐propyl‐methyl‐cellulose) in severely osteopenic and aged rats

The use of injectable biomaterials is of interest in osteoporotic patients to locally restore bone mass in sites at risk of fracture. An injectable bone substitute (IBS1 made of betaTCP/hydroxyapatite as a calcium phosphate substitute and hydroxy-propyl-methyl-cellulose as a polymer carrier) was used in a severely osteopenic rat model obtained by combining orchidectomy (ORX) and disuse (paralysis induced by botulinum toxin - BTX). Fifty-six aged male rats were randomized into three groups: 18 were SHAM operated; 38 were ORX and BTX injected in the right hindlimb; they constituted the OP (osteoporotic) group. One month after ORX-BTX surgery, 20 of these OP rats received a IBS1 injection in the right femur (OP-IBS1 rats). Animals were studied at the time of IBS1 injection 1 month post ORX-BTX (M1), 1 month (M2) and 2 months (M3) after IBS1 injection. Bone mass (BV/TV) and microarchitectural parameters were measured by microCT. BV/TV was decreased after ORX-BTX; ORX and BTX had cumulative effects on bone loss (differences maximized on the right femur). BV/TV (combining the volume of both bone and material in OP-IBS1 rats) was elevated at M1 but decreased at M2. Marked bone formation was found onto the biomaterial granules but bone had a woven texture. A marked increase in the number of nonosteoclastic TRAcP+ cells was found in the implanted area. IBS1 induced new bone formation shortly after implantation but both IBS1 and woven bone were resorbed without inducing lamellar bone. Biomaterial trials must be conducted with long-term implantation periods, in aged osteoporotic animals.

Effect of multiple ingredients on bone metabolism in the ovariectomized rat.

Whether a combination of bioactive compounds synergistically can restore bone mass needs to be explored. The objective of the present study was to examine the effects of fructoologosaccharides (FOS), a probiotic compound, by itself or in combination with green tea polyphenol (catechin), dried plum, and soy on the reversal of bone loss due to ovarian hormone deficiency. Eighty-two female 3-m old Sprague-Dawley rats were divided into eight groups (n=11) and either ovariectomized (ovx, 7 groups) or sham-operated (sham, 1 group). Rats were maintained on a semi-purified standard diet for 45 days to establish bone loss due to ovx. Thereafter, rats were placed on dietary treatments for 60 days. Treatment effects on bone mineral density (BMD) are presented below. The findings of this study indicate that the combination of Soy+FOS+Plum has the most pronounced effects in improving BMD and BMC (data not shown) in an osteopenic rat model. The microstructural analysis of proximal tibia also revealed that the same combination was able to modulate trabecular parameters such as bone volume, connectivity density, and trabecular number.

Soy moderately improves microstructural properties without affecting bone mass in an ovariectomized rat model of osteoporosis

Soy protein is reported to prevent bone loss in both women and rat models of osteoporosis. However, the role of soy isoflavones on the trabecular microarchitectural properties needs to be explored. In the present study, we examined whether soy protein with graded doses of isoflavones reverses loss of bone mineral density (BMD), bone mineral content (BMC), and trabecular microstructure in an ovariectomized (Ovx) osteopenic rat model. Seventy-eight 9-m old female Sprague–Dawley rats were either sham-operated (Sham; 1 group) or Ovx (5 groups) and fed a semi-purified casein-based diet. After 90 days, the occurrence of bone loss was confirmed using dual energy X-ray absorptiometry. Thereafter, rats were assigned to the following treatments: Sham, Ovx (control), Ovx + 17β-estradiol (E 2; 10 μg/kg body wt. twice per week), Ovx + soy protein depleted of isoflavones (Soy−; 0.06 mg isoflavones/g protein), Ovx + soy protein with normal isoflavone content (Soy; 3.55 mg isoflavones/g protein), and Ovx + isoflavone-enriched soy protein (Soy+; 7.10 mg isoflavones/g protein). After 125 days of treatment, rats were euthanized, and tibia and lumbar bones were collected for the assessment of BMD, BMC, and trabecular microarchitectural properties using X-ray microcomputed tomography. None of the treatments had an effect on BMD or microarchitectural properties of the lumbar vertebra. However, Soy treatment significantly increased tibial BMC and BMD by 10% and 4.5% compared with Ovx control, but the increase in BMD was not enough to reach the BMD levels of the Sham control group. The Soy+ diet positively affected the tibial architectural properties including trabecular thickness, separation, and number. In summary, our findings suggest that soy protein does not restore bone loss in osteopenic rats; however, higher doses of isoflavones may be required to reverse the loss of tibial microstructural properties.

Dried plum reverses bone loss in an osteopenic rat model of osteoporosis

We previously reported the efficacy of dried plum (Prunus domestica L.) in preventing ovariectomy-induced bone loss in a rat model of osteoporosis and improving bone biomarkers in postmenopausal women. The present study evaluated whether dried plum was able to restore bone mass in osteopenic ovariectomized rats. Ninety-day-old Sprague-Dawley rats were either sham-operated (Sham; one group) or ovariectomized (Ovx; five groups) and were fed a standard diet for 40 days to establish bone loss and subsequently experimental treatments were initiated. Sham, Ovx control, and Ovx + 17beta-estradiol (E2; 10 microg/kg body weight per day) animals continued to receive the standard diet, whereas the remaining three Ovx groups received the following dietary treatments: Ovx + 5% dried plum (low dose), Ovx + 15% dried plum (medium dose), and Ovx + 25% dried plum (high dose). After 60 days, blood and bone specimens were collected for analyses. Dried plum, as low as 5%, was effective in restoring femoral and tibial bone density. Dried plum increased lumbar bone density as well, with HD achieving a statistical significance. The increase in femoral bone density of dried plum-fed rats resulted in improved bone quality as indicated by 6.9% and 6.0% improvement in overall yield and ultimate force, respectively. Varying doses of dried plum were also able to significantly improve trabecular microarchitectural properties in comparison with ovariectomized controls. The improvement in biomechanical properties of long bones due to dried plum, in part, may be due to the favorable microstructural changes as evident by enhanced tibial bone volume and connectivity. Loss of bone volume accompanied by loss of trabecular connectivity is generally believed to be an irreversible process, but our observations suggest that dried plum improves trabecular microstructure of tibia after losses have already occurred.

Basic fibroblast growth factor forms new trabeculae that physically connect with pre-existing trabeculae, and this new bone is maintained with an anti-resorptive agent and enhanced with an anabolic agent in an osteopenic rat model.

Osteoporosis is a disease of excess bone fragility that results from both the loss of bone mass and trabecular bone microarchitecture, thereby creating a very fragile skeleton. The purpose of this study was to determine whether treatment of ovariectomized (OVX) osteopenic rats with basic fibroblast growth factor (bFGF) would stimulate the production of new trabeculae, and whether the newly formed trabeculae would make physical connections with the pre-existing trabeculae after prolonged estrogen deficiency. Six-month-old Sprague Dawley rats were OVXed or sham-operated and were left untreated until day 60 post-OVX. A high resolution microscopic scan (XTM) of the right proximal tibia was performed on groups 1 and 2 on day 1 post-OVX, and was repeated in all animals on day 60 post-OVX. At day 60 groups 1 and 2 were treated with vehicle and groups 3 to 6 were injected with bFGF 200 microg/kg/d intravenously for 15 days. At day 82, all animals obtained another in vivo XTM scan of the right tibia; then group 4 were treated with 17B estradiol 10 microg/kg/3x a week, group 5 were treated with hPTH (1-34) at 80 microg/kg/d for 35 days, group 6 were sacrificed, and groups 1 and 2 were treated with vehicle injections for 35 days. At day 110, all remaining animals were sacrificed, and repeat ex vivo XTM scans of the right proximal tibia were performed. Trabecular bone structural variables-including trabecular bone volume, connectivity, number, and thickness-were obtained from all XTM scans. Biochemical markers of bone turnover were also obtained 24 hours before each XTM scan (osteocalcin and deoxypyridinoline), and analyzed by ELISA. Animals OVXed and treated with vehicle had decreased trabecular bone volume, connectivity and number compared to sham-operated animals at both day 60 and day 110. Animals treated with bFGF from day 60-75 post-OVX had evidence of new trabeculae that physically connected with pre-existing trabeculae and also of increased trabecular bone volume seven days after the injections were discontinued. Biochemical markers of bone formation had a small and insignificant increase over baseline levels during the bFGF injections. Bone resorption markers were significantly reduced during the injection period, but returned to baseline levels after the injections were stopped. In addition, we also demonstrated that these newly formed trabecular connections could be maintained or added to with either estrogen or hPTH (1-34) treatments. Thirty-five days after ending the bFGF treatment, trabecular bone volume and connectivity was 25-80% higher in the estrogen and hPTH (1-34) treated animals compared to the untreated animals ( p<0.01). These results support continued development of bFGF as a potential treatment for severely osteoporotic individuals.

Effects of human PTH(1-34) and bisphosphonate on the osteopenic rat model

It has been demonstrated that the intermittent administration of human parathyroid hormone (hPTH) is beneficial for restoration of bone mass in osteoporotic patients. The mechanisms of anabolic effects of hPTH have been determined by ovariectomized rat models and other larger remodeling animals. However, treatment with hPTH may increase the cancellous bone mass at the expense of cortical bone mass and cessation of the treatment results in rapid bone loss. Efforts have been made to maintain newly formed bone mass after withdrawal of the hPTH treatment. These issues are not well understood. In this article, the authors would like to represent previous studies of their own and others concerning these issues.

W1/L2 - Effects of human PTH (1–34) and bisphosphonate on the osteopenic rat model

W1/L2 - Effects of human PTH (1–34) and bisphosphonate on the osteopenic rat model

Reactions of Bone Tissue after Placement of Implant in Osteopenic Rat Model

Reactions of Bone Tissue after Placement of Implant in Osteopenic Rat Model

A comparison of the effects of two anabolic agents (fluoride and PTH) on ash density and bone strength assessed in an osteopenic rat model

The aim of this investigation was to compare the effects of sodium fluoride (NaF) and parathyroid hormone (PTH) on ash density and strength in an osteopenic rat model. The study comprised 66 female virgin rats divided into the following 11 groups, each comprising six animals: baseline controls; baseline ovariectomized (ovx); intact controls (5 and 16 weeks), ovx controls (5 and 16 weeks); ovx-treated with PTH (0.02 mg/kg per day, 5 and 16 weeks); ovx treated with NaF (10 mg/kg per day, 5 and 16 weeks); ovx-treated with NaF (1.0 mg/kg per day, 16 weeks). Ovariectomy was performed at 12 weeks of age, 14 weeks prior to start of treatment. Ash density, bone fluoride content, and biomechanical analyses were performed on femoral cortical bone, the right femoral neck, and the sixth lumbar vertebral body. ovx had no effect on cortical bone, whereas the femoral neck displayed a significantly lower bone strength in ovx baseline animals compared with intact baseline rats ( p < 0.05). Vertebral ash density was found to be significantly decreased in ovx rats after 5 and 16 weeks ( p < 0.05). Treatment with fluoride had little effect on the osteopenic rat skeleton. Cortical ash density was significantly lower than ovx and intact groups in the high-dose-treated rats after 5 ( p < 0.01) but not after 16 weeks. High doses of fluoride for 16 weeks induced a significant increase in maximum load and normalized strength in cortical bone when compared with intact animals ( p < 0.05), but not at the other bone sites. Cortical bone strength was not different from the ovx animals at either timepoint. In fluoride-treated animals, femoral neck bone strength, vertebral body bone strength, bone quality, and ash density were found to be at about ovx levels and, in the vertebral body, significantly lower than intact animals ( p < 0.05, p < 0.01). In contrast, treatment with PTH increased ash density, bone strength, and bone quality to above ovx levels ( p < 0.01), and above the level of the intact animals also, although significant values were reached for cortical bone strength only ( p < 0.01). Additionally, biomechanical competence and ash density measurements were significantly higher in PTH-treated rats compared with fluoride-treated rats. In conclusion, this study has shown that PTH has a highly anabolic effect and is capable of effectively restoring ovx-induced loss of bone mass and biomechanical competence. In addition, in this osteopenic rat model, PTH proved much more advantageous than treatment with fluoride, which failed to restore the ovx-induced loss of bone strength.

Bone-selective analogs of human PTH(1-34) increase bone formation in an ovariectomized rat model.

Intermittent parathyroid hormone (PTH) therapy increases bone mass. The purpose of this study was to determine if analogs of human PTH(1-34) (hPTH[1-34]), which differ from the native sequence in their receptor-activating properties, could promote bone formation in an ovariectomized (OVX) osteopenic rat model. We synthesized two hPTH(1-34) analogs with single substitutions for serine in the 3-position that in vitro are partial agonists in kidney. In the renal cell line OK, maximal cyclic adenosine monophosphate (cAMP) activation by [His(3)]hPTH(134) was 50%, and maximal cAMP activation by [Leu(3)]hPTH(1-34) was 20% of that produced by hPTH(1-34). Both analogs were full agonists in UMR-106 rat osteosarcoma cells and other bone-derived systems, but both had reduced potency compared with hPTh(1-34). Six-month-old retired breeder Sprague-Dawley rats were ovariectomized, and five animals underwent sham operation. On day 56 post-OVX, five sham-operated and five pre-PTH treatment OVX animals were sacrificed, and the remaining animals were randomized into 10 groups of six animals each. All other animals were injected with one of the hPTH analogs or hPTH(1-34) at 0, 4, 40, or 400 mu g/kg of body weight (BW)/day and were killed on day 84. Histomorphometry of the proximal tibia metaphysis and biochemical markers of bone turnover (osteocalcin and pyridinoline cross-links) were the primary endpoints. The cancellous bone volume was significantly lower at day 56 post-OVX (pretreatment) and at day 84 post-OVX (post-vehicle treatment) than at baseline. None of the compounds significantly increased the cancellous bone volume. Trabecular number declined after OVX and did not change with hPTH treatment. In contrast, the trabecular thickness declined after OVX but was higher after treatment with 40 mu g/kg of BW/day or 400 mu g/kg of BW/day of hPTH(1-34). In OVX rats, the mineralizing surface was higher than baseline at day 56 and fell toward control levels by day 84. All three peptides produced marked dose-related increases in the mineralizing surface and bone formation rates, but the two analogs were less potent than hPTH(1-34). Likewise, all peptides produced significant dose-related increases in the serum osteocalcin level. The osteoclast surface was not affected by OVX but was decreased with medium and high doses of hPTH(1-34). Pyridinoline cross-link excretion was not significantly affected by treatment with hPTH(1-34) but responded with a dose-dependent decrease to treatment with [His3]hPTH(1-34). These data suggest that bone selective analogs of hPTH(1-34) maintain the ability to induce bone formation but are less potent than hPTH(1-34).

Parathyroid hormone restores bone mass and enhances osteoblast insulin-like growth factor I gene expression in ovariectomized rats

In the osteopenic rat model, estrogen deficiency results in increased bone turnover with net bone loss occurring during cancellous modeling. However, estrogen-deficient rats treated with parathyroid hormone (PTH) experience a net gain of bone tissue due to the anabolic effects of PTH. To evaluate the possibility that local insulinlike growth factor I (IGF-I) production modulates the in vivo balance of bone formation and resorption in ovariectomized (OVX) estrogen-deficient rats and in OVX rats treated with PTH, we have studied the expression of IGF-I mRNA in cancellous bone osteoblasts using in situ hybridization techniques. Three-month-old virgin rats were subjected to sham surgery or OVX. Two weeks later, half the OVX rats began treatment with hPTH(1–34), 5 gmg/100 g body weight, 5 days/week for 4 weeks. All animals were killed at the same time, providing three groups: sham surgery alone; OVX alone; and OVX + PTH. Bone histomorphometry performed in undecalcified sections of tibial metaphysis confirmed that OVX rats had significantly ( p < 0.05) increased bone surface formation rates (BFR/BS, μm 3/μm 2/year) with osteopenia while OVX + PTH rats had increased BFRBS with increased bone volumes compared to sham animals ( p < 0.05). Decalcified tissue from all three groups contained immunoreactive IGF-I. Similar tissue sections were hybridized with an 35S-labeled IGF-I antisense riboprobe. Evaluation of the specific signal over cancellous osteoblasts allowed a relative estimate of IGF-I mRNA transcript abundance in the three groups by counting silver grains per osteoblast, corrected for background activity. Despite evidence for increased BFR/BS, OVX animals had comparable frequency distributions of grain counts (after correction for background) to sham animals (88% of cells containing ⩽1 grain with a mean of 0.76 ± 0.28 grains/osteoblast vs. 81% containing ⩽1 grain with a mean of 0.61 ± 0.09, NS). However, OVX + PTH animals had over 40% of osteoblasts with ⩾2 grains per cell and twice the IGF-I mRNA abundance that either control group had (ANOVA, p < 0.001; OVX + PTH compared to either sham or OVX, p < 0.05). These data suggest tjat the anabolic effect pf PTH is associated with increased IGF-I mRNA steady state levels; while estrogen deficiency causes increase bone turnover, increased levels of IGF-I mRNA were not observed.