Alyssa A. Williams

Oncologic doses of zoledronic acid induce osteonecrosis of the jaw-like lesions in rice rats (Oryzomys palustris) with periodontitis

Though osteonecrosis of the jaw (ONJ) is temporally‐associated with the use of nitrogen‐containing bisphosphonates (N‐BPs), a cause‐and‐effect relationship has not yet been established. We hypothesize that ONJ is a two‐stage process in which: (1) risk factors initiate pathologic processes in the oral cavity that lead to a supranormal rate of hard tissue necrosis; and (2) powerful antiresorptives reduce the rate of removal of necrotic bone sufficiently to allow its net accumulation in the jaw. To test this hypothesis, we used the rice rat model of periodontitis. At age 28 days, rats (n = 15/group) were placed on a high‐sucrose and casein diet to exacerbate the development of periodontitis. Animals were injected subcutaneously (SC) biweekly with vehicle or alendronate (ALN, 15 µg/kg), or IV once monthly with vehicle, a low dose (LD) of zoledronic acid (ZOL), or a high dose (HD) of ZOL and sacrificed after 6, 12, 18, and 24 weeks. Mandibles and maxillae were analyzed to determine the effects on the: (1) progression of periodontitis; (2) integrity of alveolar bone; (3) status of bone resorption and formation; (4) vascularity; and (5) osteocyte viability. We found that only HD‐ZOL induced ONJ‐like lesions in mandibles of rice rats after 18 and 24 weeks of treatment. These lesions were characterized by areas of exposed necrotic alveolar bone, osteolysis, a honeycomb‐like appearance of the alveolar bone, presence of bacterial colonies, and periodontal tissue destruction. In addition, inhibition of bone formation, a paradoxical abolition of the antiresorptive effect of only HD‐ZOL, increased osteocyte necrosis/apoptosis, and decreased blood vessel number were found after 18 and/or 24 weeks. Our study suggests that only HD‐ZOL exacerbates the inflammatory response and periodontal tissue damage in rice rats, inducing bone lesions that resemble ONJ.

Dietary Dried Plum Increases Bone Mass in Adult and Aged Male Mice

Bone is progressively lost with advancing age. Therapies are limited and the only effective proanabolic regimen presently available to restore bone is intermittent treatment with teriparatide (parathyroid hormone 1-34). Recent evidence suggests that dietary supplementation with dried plum (DP) can prevent bone loss due to estrogen deficiency. To determine whether dietary DP supplementation can prevent the loss of bone with aging and whether bone that has already been lost can be restored, adult (6 mo) and old (18 mo) male mice were fed a normal diet or isoenergetic, isonitrogenous diets supplemented with DP (0, 15, and 25% DP by weight) for 6 mo. MicroCT analysis and bone histomorphometry were used to assess bone volume, structure, and metabolic activity before, during, and after dietary supplementation. Mice fed the 0% DP diet (control diet) lost bone, whereas both adult and old mice fed the 25% DP-supplemented diet gained bone. Adult but not old mice fed the 15% diet also gained bone. Cancellous bone volume in mice receiving 25% DP exceeded baseline levels by 40-50%. Trabecular structure varied with diet and age and responses in old mice were generally blunted. Trabecular, but not cortical, mineral density varied with age and measures of bone anabolic activity were lower in aged mice. Our findings suggest that DP contains proanabolic factors that can dramatically increase bone volume and restore bone that has already been lost due to aging. In turn, DP may provide effective prophylactic and therapeutic agents for the treatment of osteoporosis.

SCLEROSTIN INHIBITION PREVENTS SPINAL CORD INJURY INDUCED CANCELLOUS BONE LOSS

Spinal cord injury (SCI) results in rapid and extensive sublesional bone loss. Sclerostin, an osteocyte‐derived glycoprotein that negatively regulates intraskeletal Wnt signaling, is elevated after SCI and may represent a mechanism underlying this excessive bone loss. However, it remains unknown whether pharmacologic sclerostin inhibition ameliorates bone loss subsequent to SCI. Our primary purposes were to determine whether a sclerostin antibody (Scl‐Ab) prevents hindlimb cancellous bone loss in a rodent SCI model and to compare the effects of a Scl‐Ab to that of testosterone‐enanthate (TE), an agent that we have previously shown prevents SCI‐induced bone loss. Fifty‐five (n = 11–19/group) skeletally mature male Sprague‐Dawley rats were randomized to receive: (A) SHAM surgery (T8 laminectomy), (B) moderate‐severe (250 kilodyne) SCI, (C) 250 kilodyne SCI + TE (7.0 mg/wk, im), or (D) 250 kilodyne SCI + Scl‐Ab (25 mg/kg, twice weekly, sc) for 3 weeks. Twenty‐one days post‐injury, SCI animals exhibited reduced hindlimb cancellous bone volume at the proximal tibia (via μCT and histomorphometry) and distal femur (via μCT), characterized by reduced trabecular number and thickness. SCI also reduced trabecular connectivity and platelike trabecular structures, indicating diminished structural integrity of the remaining cancellous network, and produced deficits in cortical bone (femoral diaphysis) strength. Scl‐Ab and TE both prevented SCI‐induced cancellous bone loss, albeit via differing mechanisms. Specifically, Scl‐Ab increased osteoblast surface and bone formation, indicating direct bone anabolic effects, whereas TE reduced osteoclast surface with minimal effect on bone formation, indicating antiresorptive effects. The deleterious microarchitectural alterations in the trabecular network were also prevented in SCI + Scl‐Ab and SCI + TE animals, whereas only Scl‐Ab completely prevented the reduction in cortical bone strength. Our findings provide the first evidence indicating that sclerostin inhibition represents a viable treatment to prevent SCI‐induced cancellous and cortical bone deficits and provides preliminary rationale for future clinical trials focused on evaluating whether Scl‐Ab prevents osteoporosis in the SCI population.

Influence of Aromatase Inhibition on the Bone‐Protective Effects of Testosterone

The influence of the aromatase enzyme in androgen‐induced bone maintenance after skeletal maturity remains somewhat unclear. Our purpose was to determine whether aromatase activity is essential to androgen‐induced bone maintenance. Ten‐month‐old male Fisher 344 rats (n = 73) were randomly assigned to receive Sham surgery, orchiectomy (ORX), ORX + anastrozole (AN; aromatase inhibitor), ORX + testosterone‐enanthate (TE, 7.0 mg/wk), ORX + TE + AN, ORX + trenbolone‐enanthate (TREN; nonaromatizable, nonestrogenic testosterone analogue; 1.0 mg/wk), or ORX + TREN + AN. ORX animals exhibited histomorphometric indices of high‐turnover osteopenia and reduced cancellous bone volume compared with Shams. Both TE and TREN administration suppressed cancellous bone turnover similarly and fully prevented ORX‐induced cancellous bone loss. TE‐ and TREN‐treated animals also exhibited greater femoral neck shear strength than ORX animals. AN co‐administration slightly inhibited the suppression of bone resorption in TE‐treated animals but did not alter TE‐induced suppression of bone formation or the osteogenic effects of this androgen. In TREN‐treated animals, AN co‐administration produced no discernible effects on cancellous bone turnover or bone volume. ORX animals also exhibited reduced levator ani/bulbocavernosus (LABC) muscle mass and elevated visceral adiposity. In contrast, TE and TREN produced potent myotrophic effects in the LABC muscle and maintained fat mass at the level of Shams. AN co‐administration did not alter androgen‐induced effects on muscle or fat. In conclusion, androgens are able to induce direct effects on musculoskeletal and adipose tissue, independent of aromatase activity.

Enhanced alveolar bone loss in a model of non-invasive periodontitis in rice rats.

OBJECTIVE The rice rat (Oryzomys palustris) develops periodontitis-like lesions when fed a diet rich in sucrose and casein (H-SC). We aimed to establish whether this model can accurately mimic the development of human periodontitis. MATERIALS AND METHODS For this purpose, 28-day-old rice rats (15/group) were assigned to standard (STD) or H-SC diets and sacrificed after 6, 12, and 18 weeks. Jaws were processed for morphometric, histometric, histologic, histomorphometric, and micro-CT analyses. RESULTS We found a progressive increase in horizontal alveolar bone loss (ABL) with age in maxillae of rats fed the STD diet as determined by morphometry. The H-SC diet exacerbated horizontal ABL at the palatal surface at 12 and 18 weeks. Furthermore, increased vertical ABL was detected in mandibles and maxillae of rats fed the H-SC diet for 12 and/or 18 weeks by histometry and micro-CT. Remarkably, the H-SC diet significantly increased bone remodeling at the interproximal alveolar bone of mandibles from rats fed for 6 weeks, but not in those fed for longer periods. CONCLUSIONS These findings indicate that the H-SC diet induced a transient increase in alveolar bone remodeling, which is followed by ABL characteristic of moderate periodontitis.

A rehabilitation exercise program induces severe bone mineral deficits in estrogen-deficient rats after extended disuse.

ObjectiveBoth estrogen and mechanical loading regulate bone maintenance. However, mechanical overload seems less effective in enhancing bone mineral density (BMD) in estrogen-deficient women. The aim of this study was to determine whether estradiol (E2) influences early-phase bone adaptations to reambulation (REAMB) and/or rehabilitation exercises after hindlimb unloading (HLU) of ovariectomized rats. MethodsEighty-one 5-month-old female Sprague-Dawley rats were randomized into the following groups: (1) intact controls, (2) ovariectomy (OVX), (3) OVX + E2, (4) OVX + 4 weeks of HLU, (5) OVX + E2 + HLU, (6) OVX + HLU + 2 weeks of quadrupedal REAMB, (7) OVX + E2 + HLU + REAMB, (8) OVX + HLU + REAMB + supplemental climbing, jumping, and balance exercises (EX), or (9) OVX + E2 + HLU + REAMB + EX. Serial dual-energy x-ray absorptiometry scans were performed to track total body bone characteristics throughout the study, and peripheral quantitative computerized tomography was used to determine distal femoral metaphyseal bone mineral characteristics. ResultsTotal body BMD increased by 4% to 8% in all animals receiving supplemental E2, whereas BMD did not change in animals without E2. OVX reduced trabecular BMD at the femoral metaphysis, and HLU exacerbated this loss while also reducing cortical BMD. E2 protected against OVX + HLU–induced bone loss at the femoral metaphysis. Conversely, REAMB did not alter BMD, regardless of estrogen status. In the absence of E2, REAMB + EX resulted in severe bone loss after OVX + HLU, with trabecular BMD and cortical BMD measurements that were 91% and 7% below those of controls, respectively (P ⩽ 0.001). However, in the presence of E2, REAMB + EX did not negatively influence bone mineral characteristics. ConclusionsE2 protects against bone loss resulting from combined OVX + HLU of rodents. In the absence of estrogen, exercise induces disadvantageous early-phase bone adaptations after extended disuse.

Age-related periodontitis and alveolar bone loss in rice rats

OBJECTIVE To characterize in rice rats: (a) periodontitis (PD) progress with feeding of standard laboratory rat chow (STD) during ages 4-80 weeks; and (b) PD progress with feeding of a high sucrose-casein (H-SC) diet during young adulthood. METHODS One group (N=12) was euthanized at age 4 weeks (Baseline). Four groups (N=8-16) consumed a STD diet from baseline and were necropsied at ages 22, 30, 52, and 80 weeks. Three groups (N=10-16) consumed an H-SC diet from baseline. Two were necropsied at ages 22 and 30 weeks, respectively. The third switched to the STD diet at age 22 weeks and was necropsied at age 30 weeks. All mandibles/maxillae were assessed by histometry for degree of periodontal inflammation (PD Score), alveolar crest height (ACH, mm), and horizontal alveolar bone height (hABH, mm2). RESULTS In STD diet rats aged ≥30 weeks, all endpoints were worse (P<0.05) than at Baseline. In H-SC diet rats aged ≥22 weeks, all endpoints were worse than at Baseline (P<0.05). At age 22 weeks, all endpoints were worse in the H-SC group than in the STD group (P<0.05). By age 30 weeks, the STD and H-SC groups did not differ. CONCLUSIONS 1) STD diet fed rice rats develop moderate/severe PD by age 30 weeks; 2) an H-SC diet accelerates moderate/severe PD development; and 3) switching to a STD diet does not halt/reverse PD that was accelerated by an H-SC diet. These data further clarify use of the rice rat as a PD model.