Bone Structural, Biomechanical and Histomorphometric Characteristics of the Hindlimb Skeleton in the Marsh Rice Rat (Oryzomys palustris)

INTRODUCTION

The rice rat (Oryzomys palustris) is a non-conventional laboratory rodent species used to model some human bone disorders. However, no studies have been conducted to characterize the postcranial skeleton. Therefore, we aimed to investigate age- and gender-related features of the hindlimb skeleton of this species.

METHODS

We used femurs and tibiae from 94 rats of both genders aged 4-28 wks. Bone mineral content (BMC), volumetric bone mineral density (vBMD), and biomechanical properties were determined in femurs. In addition, bone histomorphometry of tibiae was conducted to assess bone cell activities and bone turnover over time.

RESULTS

Bone length, total metaphysis BMC and vBMD, mid-diaphyseal BMC and vBMD, cortical thickness, and cortical area progressively augmented with age. Whereas the increase in these parameters plateaued at age 16-22 wks in female rats, they continued to rise to age 28 wks in male rats. Furthermore, bone strength parameters increased with age, with few differences between genders. We also observed a rapid decrease in longitudinal growth between ages 4-16 wks. Whereas young rats had a greater bone formation rate and bone turnover, older rice rats had greater bone volume and trabecular thickness, with no differences between genders.

CONCLUSIONS

1) Sexual dimorphism in the rice rat becomes grossly evident at age 16 wks; 2) the age-related increases in bone mass, structural cortical parameters, and in some biomechanical property parameters plateau at an older age in male than in female rats; and 3) bone growth and remodeling significantly decreased with age irrespective of the gender.

Biologic and pathologic aspects of osteocytes in the setting of medication-related osteonecrosis of the jaw (MRONJ)

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe, debilitating condition affecting patients with cancer and patients with osteoporosis who have been treated with powerful antiresorptives (pARs) or angiogenesis inhibitors (AgIs). Oral risk factors associated with the development of MRONJ include tooth extraction and inflammatory dental disease (e.g., periodontitis, periapical infection). In bone tissues, osteocytes play a bidirectional role in which they not only act as the "receiver" of systemic signals from blood vessels, such as hormones and drugs, or local signals from the mineralized matrix as it is deformed, but they also play a critical role as "transmitter" of signals to the cells that execute bone modeling and remodeling (osteoclasts, osteoblasts and lining cells). When the survival capacity of osteocytes is overwhelmed, they can die. Osteocyte death has been associated with several pathological conditions. Whereas the causes and mechanisms of osteocyte death have been studied in conditions like osteonecrosis of the femoral head (ONFH), few studies of the causes and mechanisms of osteocyte death have been done in MRONJ. The three forms of cell death that affect most of the different cells in the body (apoptosis, autophagy, and necrosis) have been recognized in osteocytes. Notably, necroptosis, a form of regulated cell death with "a necrotic cell death phenotype," has also been identified as a form of cell death in osteocytes under certain pathologic conditions. Improving the understanding of osteocyte death in MRONJ may be critical for preventing disease and developing treatment approaches. In this review, we intend to provide insight into the biology of osteocytes, cell death, in general, and osteocyte death, in particular, and discuss hypothetical mechanisms involved in osteocyte death associated with MRONJ.

Preclinical models of medication-related osteonecrosis of the jaw (MRONJ)

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe adverse event affecting patients with cancer and patients with osteoporosis who have been treated with powerful antiresorptives (pARs) or angiogenesis inhibitors (AgIs). pARs, including nitrogen-containing bisphosphonates (N-BPs; e.g., zoledronic acid, alendronate) and anti-RANKL antibodies (e.g., denosumab), are used to manage bone metastases in patients with cancer or to prevent fragility fractures in patients with osteoporosis. Though significant advances have been made in understanding MRONJ, its pathophysiology is still not fully elucidated. Multiple species have been used in preclinical MRONJ research, including the rat, mouse, rice rat, rabbit, dog, sheep, and pig. Animal research has contributed immensely to advancing the MRONJ field, particularly, but not limited to, in developing models and investigating risk factors that were first observed in humans. MRONJ models have been developed using clinically relevant doses of systemic risk factors, like N-BPs, anti-RANKL antibodies, or AgIs. Specific local oral risk factors first noted in humans, including tooth extraction and inflammatory dental disease (e.g., periodontitis, periapical infection, etc.), were then added. Research in rodents, particularly the rat, and, to some extent, the mouse, across multiple laboratories, has contributed to establishing multiple relevant and complementary preclinical models. Models in larger species produced accurate clinical and histopathologic outcomes suggesting a potential role for confirming specific crucial findings from rodent research. We view the current state of animal models for MRONJ as good. The rodent models are now reliable enough to produce large numbers of MRONJ cases that could be applied in experiments testing treatment modalities. The course of MRONJ, including stage 0 MRONJ, is characterized well enough that basic studies of the molecular or enzyme-level findings in different MRONJ stages are possible. This review provides a current overview of the existing models of MRONJ, their more significant features and findings, and important instances of their application in preclinical research.

Preventing or controlling periodontitis reduces the occurrence of osteonecrosis of the jaw (ONJ) in rice rats (Oryzomys palustris)

INTRODUCTION

Osteonecrosis of the jaw (ONJ) is an adverse event that requires association of both systemic risk factors, such as powerful anti-resorptives (pARs; e.g. zoledronic acid [ZOL]), and local oral risk factors (e.g. tooth extraction, periodontitis). Whereas optimal oral health prior to initiate pARs is recognized as critically important for minimizing ONJ risk, the efficacy of preventive/maintenance measures in patients who are taking pARs is understudied. Rice rats fed a standard diet (STD), rich in insoluble fiber, develop localized periodontitis. STD-rats with localized periodontitis treated with ZOL for 18-24 wk develop ONJ. Hence, we hypothesized that controlling/preventing localized periodontitis in the ZOL-treated rats, reduces ONJ occurrence.

METHODS

We used two approaches to attempt reducing periodontitis prevalence: 1) periodontal cleaning (PC); and 2) replacing the STD-diet with a nutritionally-equivalent diet high in soluble fiber (SF). 75 four-week-old male rats were weight-randomized into five groups (n = 15) in a 24-week experiment. Three groups ate the STD-diet and two the high SF-diet. STD-diet groups received intravenous (IV) vehicle (VEH) q4wks (STD + VEH), 80 μg/kg ZOL q4wks IV (STD + ZOL), or ZOL plus PC q2wks (STD + ZOL + PC). The SF-diet groups received VEH (SF + VEH) or ZOL (SF + ZOL). Jaws were processed for histopathology and evaluated for ONJ prevalence and tissue-level periodontitis.

RESULTS

1) 40% of STD + VEH rats developed maxillary localized periodontitis with no ONJ; 2) 50% of STD + ZOL rats developed ONJ; 3) 7% of STD + ZOL + PC rats developed ONJ (p < 0.01 vs. STD + ZOL); and 4) one SF + ZOL rat developed localized periodontitis, and no SF + VEH or SF + ZOL rats developed ONJ (p < 0.001 vs. STD + ZOL).

CONCLUSIONS

1) Periodontal cleaning in ZOL-treated rats decreases localized periodontitis severity and reduces ONJ prevalence; and 2) feeding a SF-diet to ZOL-treated rats reduces both incidence of localized periodontitis and ONJ. Our data indicates strong oral microbial community shifts according to oral health condition and trends in the shifts associated with diet.

The beta-glucuronidase intracisternal A particle insertion model results in similar overall MPSVII phenotype as the single base deletion model when on the same C57BL/6J mouse background

Two unique gene mutations in the enzyme beta-glucuronidase (GUSB) that result in the lysosomal storage disease Mucopolysaccharidosis (MPS) type VII had previously been reported to have differing disease phenotype severities when compared on differing mouse strains. The MPSVII mouse has proven to be a highly efficacious model to study mucopolysaccharidoses and for evaluating potential gene or stem cell therapies for lysosomal storage diseases. We examined the single base pair deletion (MPSVII) and the intracisternal A particle element insertion (MPSVII2J) in GUSB compared with control animals by skeletal measures, electroretinography, auditory-evoked brainstem response and life span on a C57BL/6J background strain. In all measures, both mutations result in either a trend toward or significant changes from the background strain control. In all measures, there is no significant phenotypic difference between the two mutations. The 2J variant is a more easily genotyped and equally affected phenotype, which holds promise for further studies of chimerism and stem cell therapy approaches.

Anti-vascular endothelial growth factor antibody monotherapy causes destructive advanced periodontitis in rice rats (Oryzomys palustris)

OBJECTIVE

Angiogenesis inhibitors (AgI) are commonly used in combination chemotherapy protocols to treat cancer, and have been linked to osteonecrosis of the jaw (ONJ). However, it is unknown if AgI therapy alone is sufficient to induce ONJ. We have previously established an ONJ model in rice rats with localized periodontitis that receive zoledronic acid (ZOL). The purpose of this study was to use this model to determine the role of anti-vascular endothelial growth factor A (anti-VEGF) antibody treatment of rice rats with localized maxillary periodontitis. We hypothesized that rice rats with localized maxillary periodontitis given anti-VEGF monotherapy will develop oral lesions that resemble ONJ, defined by exposed, necrotic alveolar bone.

METHODS

At age 4 weeks, 45 male rice rats were randomized into three groups (n = 15): 1) VEH (saline), 2) ZOL (80 μg/kg body weight, intravenously once monthly), and 3) anti-VEGF (5 mg B20-4.1.1/kg body weight, subcutaneously twice weekly). After 24 weeks, rats were euthanized, jaws were excised and a high-resolution photograph of each quadrant was taken to assign a severity grade based on gross appearance. Jaws were then fixed, scanned by MicroCT, decalcified and sectioned for histopathologic and immunohistochemical analyses.

RESULTS

40-80% of the rats in the three groups developed gross oral lesions. 50% of ZOL rats developed ONJ. In contrast, 80% of the anti-VEGF rats developed destructive advanced periodontitis that was characterized by extreme alveolar bone loss and fibrosis. Anti-VEGF rats never developed exposed, necrotic bone. Furthermore, only anti-VEGF rats developed mild to severe mandibular periodontitis. Compared to VEH rats, more T-cells were found in periodontal lesions of anti-VEGF rats and more cells of the monocyte lineage were found in ONJ lesions of ZOL rats.

CONCLUSIONS

Anti-VEGF monotherapy administered to a validated rodent model of ONJ caused a destructive advanced form of periodontitis that differed significantly from ONJ.

Locomotor training with adjuvant testosterone preserves cancellous bone and promotes muscle plasticity in male rats after severe spinal cord injury

Loading and testosterone may influence musculoskeletal recovery after spinal cord injury (SCI). Our objectives were to determine (a) the acute effects of bodyweight-supported treadmill training (TM) on hindlimb cancellous bone microstructure and muscle mass in adult rats after severe contusion SCI and (b) whether longer-term TM with adjuvant testosterone enanthate (TE) delivers musculoskeletal benefit. In Study 1, TM (40 min/day, 5 days/week, beginning 1 week postsurgery) did not prevent SCI-induced hindlimb cancellous bone loss after 3 weeks. In Study 2, TM did not attenuate SCI-induced plantar flexor muscles atrophy nor improve locomotor recovery after 4 weeks. In our main study, SCI produced extensive distal femur and proximal tibia cancellous bone deficits, a deleterious slow-to-fast fiber-type transition in soleus, lower muscle fiber cross-sectional area (fCSA), impaired muscle force production, and levator ani/bulbocavernosus (LABC) muscle atrophy after 8 weeks. TE alone (7.0 mg/week) suppressed bone resorption, attenuated cancellous bone loss, constrained the soleus fiber-type transition, and prevented LABC atrophy. In comparison, TE+TM concomitantly suppressed bone resorption and stimulated bone formation after SCI, produced near-complete cancellous bone preservation, prevented the soleus fiber-type transition, attenuated soleus fCSA atrophy, maintained soleus force production, and increased LABC mass. 75% of SCI+TE+TM animals recovered voluntary over-ground hindlimb stepping, while no SCI and only 20% of SCI+TE animals regained stepping ability. Positive associations between testosterone and locomotor function suggest that TE influenced locomotor recovery. In conclusion, short-term TM alone did not improve bone, muscle, or locomotor recovery in adult rats after severe SCI, while longer-term TE+TM provided more comprehensive musculoskeletal benefit than TE alone.

Potential therapeutic use of relaxin in accelerating closure of cranial bone defects in mice

Bone fractures are associated with considerable morbidity and increased mortality. A major limitation to healing is lack of bone blood flow, which is impaired by physical disruption of intraskeletal and/or periosteal vasculature by the fracture. Thus, pharmacological interventions are needed to improve osseous blood flow, thereby accelerating bone fracture closure. Relaxin is secreted by the ovary and circulates in rodents and humans during pregnancy. Because relaxin might benefit bone fracture healing by stimulating angiogenesis, vasculogenesis (and potentially osteogenesis) through mobilization and activation of bone marrow progenitor cells, and by increasing blood flow via vasodilation, we investigated whether relaxin administration would accelerate closure of a calvarial defect in mice. Whether administered systemically by osmotic pump or locally by collagen scaffolds for ~2 week period after lesioning, relaxin did not accelerate bone healing. Despite implementing relaxin doses that reached plasma concentrations spanning the physiological to supraphysiological range, testing the closure of two different sizes of calvarial lesions, allowing for different intervals of time from instigation of cranial lesion to euthanasia, and investigating mice of different ages, we did not observe a significant benefit of relaxin in bone lesion healing. Nor did we observe stimulation of blood vessel formation in the bone lesion by the hormone. An incidental finding was that relaxin appeared to enhance trabecular bone growth in an uninjured control bone (femur). Although the results of this study were not supportive of a therapeutic benefit for relaxin on calvarial defect closure, future investigation is needed employing different animal species and experimental models of bone fracture.

Inhibition of vascular endothelial growth factor in young adult mice causes low bone blood flow and bone strength with no effect on bone mass in trabecular regions

Objective

To determine the effect of an antibody to vascular endothelial growth factor (VEGF) on bone blood flow, bone strength, and bone mass in the young adult mouse.

Methods

Ten-week-old male BALB/cJ mice were body weight-randomized into either a rodent anti-VEGF monoclonal antibody (anti-VEGF, B20-4.1.1; 5 mg/kg 2×/wk.; n = 12) group or a vehicle (VEH; n = 12) group. After 42 days, mice were evaluated for bone blood flow at the distal femur by ¹⁸F-NaF-PET/CT and then necropsied. Samples from trabecular and cortical bone regions were evaluated for bone strength by mechanical testing, bone mass by peripheral quantitative computed tomography (pQCT), and micoarchitecture (MicroCT). Hydration of the whole femur was studied by proton nuclear magnetic resonance relaxometry (¹H NMR).

Results

Distal femur blood flow was 43% lower in anti-VEGF mice than in VEH mice (p = 0.009). Ultimate load in the lumbar vertebral body was 25% lower in anti-VEGF than in VEH mice (p = 0.013). Bone mineral density (BMD) in the trabecular region of the proximal humeral metaphysis by pQCT, and bone volume fraction and volumetric BMD by MicroCT were the same in the two groups. Volume fraction of bound water (BW) of the whole femur was 14% lower in anti-VEGF than in VEH mice (p = 0.003). Finally, BW, but not cortical tissue mineral density, helped section modulus explain the variance in the ultimate moment experienced by the femur in three-point bending.

Conclusion

Anti-VEGF caused low bone blood flow and bone strength in trabecular bone regions without influencing BMD and microarchitecture. Low bone strength was also associated with low bone hydration. These data suggest that bone blood flow is a novel bone property that affects bone quality.

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An antibody to vascular endothelial growth factor (anti-VEGF) caused low bone blood flow in a trabecular bone rich region.

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Anti-VEGF did not affect trabecular bone region and bone hydration of the whole femur were also low, trabecular bone mass was not affected by anti-VEGF.

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Bone blood flow may be a bone property that affects bone quality through bone hydration.

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Anti-VEGF caused low trabecular bone strength in the vertebral body and low bone hydration of the whole femur.

Impaired innate immune signaling due to combined Toll-like receptor 2 and 4 deficiency affects both periodontitis and atherosclerosis in response to polybacterial infection

Plasma membrane-associated Toll-like receptor (TLR2 and TLR4) signaling contributes to oral microbe infection-induced periodontitis and atherosclerosis. We recently reported that either TLR2 or TLR4 receptor deficiency alters recognition of a consortium of oral pathogens, modifying host responses in periodontitis and atherosclerosis. We evaluated the effects of combined TLR2-/-TLR4-/- double knockout mice on innate immune signaling and induction of periodontitis and atherosclerosis after polybacterial infection with Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia and Fusobacterium nucleatum in a mouse model. Multispecies infections established gingival colonization in all TLR2-/-TLR4-/- mice and induced production of bacterial-specific IgG antibodies. In combined TLR2-/-TLR4-/- deficiency there was, however, reduced alveolar bone resorption and mild gingival inflammation with minimal migration of junctional epithelium and infiltration of inflammatory cells. This indicates a central role for TLR2 and TLR4 in periodontitis. Atherosclerotic plaque progression was markedly reduced in infected TLR2-/-TLR4-/- mice or in heterozygotes indicating a profound effect on plaque growth. However, bacterial genomic DNA was detected in multiple organs in TLR2-/-TLR4-/- mice indicating an intravascular dissemination from gingival tissue to heart, aorta, kidney and lungs. TRL2 and TLR4 were dispensable for systemic spread after polybacterial infections but TLR2 and 4 deficiency markedly reduces atherosclerosis induced by oral bacteria.

Exosomes: novel regulators of bone remodelling and potential therapeutic agents for orthodontics

Recent studies suggest that exosomes are involved in intercellular communication required for the maintenance of healthy bone. Exosomes are small (30-150 nm in diameter) extracellular vesicles that are formed in multivesicular bodies and are released from cells as the multivesicular bodies fuse with the plasma membrane. Regulatory exosomes have the capacity to exert profound control over target cells. They can stimulate plasma membrane receptors and are also internalized by the target cell delivering proteins, lipids, small molecules and functional RNAs from the cell of origin. We and others have recently reported on regulatory exosomes from osteoclasts and osteoblasts. Key candidate molecules identified in exosome-based regulation of bone remodelling include receptor activator of nuclear factor kappa B (RANK), RANK-ligand (RANKL), ephrinA2, semaphorin 4D, microRNA-146a and microRNA- 214-3p. Exosomes will likely prove to be crucial elements in the communication networks integrating bone cells (osteoclasts, osteoblasts, osteocytes) and linking bone to other tissue. Exosomes collected from bone cells grown in culture may prove useful to augment bone remodelling associated with orthodontic force application or required for the repair of craniofacial bone. Various technologies allow exosomes to be engineered to improve their targeting and efficacy for therapeutic purposes. In summary, exosomes have emerged as important elements of the machinery for intercellular communication between bone cells. They hold great promise as therapeutic targets, biomarkers and therapeutic agents for orthodontists.

Zoledronic acid increases the prevalence of medication-related osteonecrosis of the jaw in a dose dependent manner in rice rats (Oryzomys palustris) with localized periodontitis

OBJECTIVE

Investigate role of dose/duration of zoledronic acid (ZOL), a powerful anti-resorptive (pAR), on prevalence of medication-related osteonecrosis of the jaw (MRONJ) in rice rats (Oryzomys palustris), a species with natural susceptibility to food impaction-induced localized periodontitis (FILP). We hypothesize that ZOL induces MRONJ lesions in rice rats with FILP, and that the prevalence of MRONJ rises with increasing dose and duration of ZOL treatment.

METHODS

We performed a toxicology experiment with clinically-relevant doses of ZOL in female rats (N=230) fed standard (STD) rodent chow. At age 4weeks (baseline), 12 rats were necropsied. The rest were randomized into five groups that began to receive 0, 8, 20, 50 or 125μg/kg ZOL IV/q 4weeks. After 12, 18, 24 and 30weeks, subgroups (N=9-16) from each of the dose groups were necropsied. High-resolution macroscopic photos of all jaw quadrants were given a gross quadrant grade (GQG) (0-4 or MRONJ) that classified FILP lesion severity and determined presence of gross MRONJ. Quadrants with GQG≥1 were examined histopathologically. Logistic regression analysis (ZOL dose/duration) of MRONJ prevalence was completed.

RESULTS

We found: 1) 75% of 0μg/kg ZOL rats developed FILP lesions; 2) baseline rats and rats treated with 0μg/kg ZOL had no MRONJ; 3) 29 gross MRONJ cases were identified; 4) all gross MRONJ cases were confirmed histopathologically by the observation of exposed necrotic bone, and 53 new cases were discovered (total=82); 5) ZOL dose (P<0.001), but not duration (P=0.326), was a significant predictor of MRONJ prevalence; 6) 13% prevalence of gross MRONJ among all rats, with 22% prevalence among rats exposed to ZOL oncologic doses (20-125μg/kg); 7) 38% prevalence of histopathologic MRONJ among all rats, with 73% prevalence among rats exposed to ZOL oncologic doses.

CONCLUSIONS

This is the first experiment to show a dose response relationship between clinically relevant doses of ZOL and MRONJ prevalence.

Bone Mass Is Compromised by the Chemotherapeutic Trabectedin in Association With Effects on Osteoblasts and Macrophage Efferocytosis

Macrophages have established roles supporting bone formation. Despite their professional phagocytic nature, the role of macrophage phagocytosis in bone homeostasis is not well understood. Interestingly, apoptosis is a pivotal feature of cellular regulation and the primary fate of osteoblasts is apoptosis. Efferocytosis (phagocytosis of apoptotic cells) is a key physiologic process for the homeostasis of many tissues, and is associated with expression of osteoinductive factors. To test effects of macrophage depletion and compromised phagocytosis on bone, 16-week-old male C57BL/6J mice were treated with trabectedin-a chemotherapeutic with established anti-macrophage effects. Trabectedin treatment reduced F4/80+ and CD68+ macrophages in the bone marrow as assessed by flow cytometry, osteal macrophages near the bone surface, and macrophage viability in vitro. Trabectedin treatment significantly reduced marrow gene expression of key phagocytic factors (Mfge8, Mrc1), and macrophages from treated mice had a reduced ability to phagocytose apoptotic mimicry beads. Macrophages cultured in vitro and treated with trabectedin displayed reduced efferocytosis of apoptotic osteoblasts. Moreover, efferocytosis increased macrophage osteoinductive TGF-β production and this increase was inhibited by trabectedin. Long-term (6-week) treatment of 16-week-old C57BL/6J mice with trabectedin significantly reduced trabecular BV/TV and cortical BMD. Although trabectedin reduced osteoclast numbers in vitro, osteoclast surface in vivo was not altered. Trabectedin treatment reduced serum P1NP as well as MS/BS and BFR/BS, and inhibited mineralization and Runx2 gene expression of osteoblast cultures. Finally, intermittent PTH 1-34 (iPTH) treatment was administered in combination with trabectedin, and iPTH increased trabecular bone volume fraction (BV/TV) in trabectedin-treated mice. Collectively, the data support a model whereby trabectedin significantly reduces bone mass due to compromised macrophages and efferocytosis, but also due to direct effects on osteoblasts. This data has immediate clinical relevance in light of increasing use of trabectedin in oncology. © 2017 American Society for Bone and Mineral Research.

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.

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.

Effects of alendronate on bone healing after tooth extraction in rats

OBJECTIVES

Tooth extraction has been identified as an important risk factor for bisphosphonate-induced osteonecrosis of the jaw. Therefore, the main goal of this study was to determine the effects of alendronate on healing of the extraction socket and on interdental alveolar bone after tooth extraction in rats.

MATERIALS AND METHODS

Animals were injected subcutaneously with vehicle or alendronate for 3-4 weeks before the first mandibular molar was extracted and these treatments were continued during post-extraction periods of 10, 21, 35 and 70 days. Mandibles were processed to evaluate healing of the extraction socket and adjacent alveolar bone by assessing bone formation, bone resorption and vascularity by histomorphometric techniques.

RESULTS

Alendronate decreased new woven bone formation, blood vessel area, perimeter and number in the extraction socket at 10 days postextraction, but not at later time points. Furthermore, alendronate-treated rats had increased interdental alveolar bone volume and height only at 10 days postextraction. In addition, a 2.5-fold increase in the percentage of empty osteocyte lacunae was found in alveolar bone of alendronate-treated rats only at 10 days postextraction.

CONCLUSIONS

Alendronate transiently decreases bone formation and vascularity in the extraction socket and delays the removal of interdental alveolar bone after tooth extraction in rats.

Does breeding status influence haematology and blood biochemistry of yellow-legged gulls?

We compared the haematological and biochemical values within a population of yellow-legged gulls (Larus michahellis) in the Chafarinas Islands (Northern Africa), in non-breeding (February) and breeding (May) animals. We collected blood samples from 51 adults. We found that according to the haematological data, there was a significant variation in haemoglobin content, and a higher proportion of heterophils, thrombocytes, and Haemoproteus infection in breeding individuals with a lower level in basophils. Blood biochemistry showed a higher level in plasmatic proteins, calcium, phosphorus, thiobarbituric acidreactive substances and alkaline phosphatase as well as alanine aminotransferase activity in breeding animals while cholesterol and phospholipid levels showed a lower level. There was also a sexual difference in triglycerides, albumin, thiobarbituric acid-reactive substances and alkaline phosphatase activity. Hence, the haematological and blood chemistry values of yellow-legged gulls showed some differences between breeding and non-breeding individuals as well as between sexes.

In vitro and in vivo evidence for stimulation of bone resorption by an EP4 receptor agonist and basic fibroblast growth factor: Implications for their efficacy as bone anabolic agents

Prostaglandin E2 receptor subtype 4 agonists (EP4A) and basic fibroblast growth factor (FGF2) stimulate bone formation, but their effects on bone resorption are controversial. To provide additional insight into the skeletal effects of EP4A and FGF2, their regulation of expression of genes associated with bone formation and resorption in aged ovariectomized (OVX) rats and in cultured mouse bone marrow cells was determined. RNA was isolated from lumbar vertebrae of OVX rats (16 months of age) treated daily for 3 weeks with FGF2 or EP4A and processed for quantitative real time-PCR analyses. mRNA expression for the receptor activator of NF-kappaB ligand (RANKL) and cathepsin K (CTSK), but not osteoprotegerin (OPG), were upregulated by both FGF2 and EP4A. Addition of FGF2 and EP4A to the medium of cultured mouse bone marrow cells increased the formation of tartrate resistant acid phosphatase (TRAP) positive cells, upregulated the expression of RANKL and CTSK, and downregulated expression for OPG. EP4A also increased the formation of actin rings, an indicator of osteoclast activation, in a dose dependent manner in osteoclasts cultured on bone slices and triggered the formation of pits as revealed by a pitting assay. Gene expression for osterix (OSX) and IGF-2, genes associated with bone formation, was significantly greater in FGF2-treated OVX rats compared with EP4A-treated OVX rats. These findings at the molecular level are consistent with previous tissue-level histomorphometric findings, and at the doses tested, support the contention that FGF2 has a stronger bone anabolic effect than EP4A. The results of these in vivo and in vitro analyses clarify the effects of FGF2 and EP4A on bone formation and resorption, and provide insight into differences in the efficacy of two potential bone anabolic agents for restoration of lost bone mass in the osteopenic, estrogen-deplete skeleton.

Skeletal effects of fibroblast growth factor mimetic (F2A) in ovariectomized rats

The current study was designed to determine whether short-term, systemic treatment with F2A, a mimetic for FGF-2, has skeletal effects in ovariectomized (OVX) rats and adverse side effects in non-skeletal tissues. Groups of sham-operated and OVX rats were maintained untreated for 6 weeks postOVX. These groups (N=6) were then treated IP with vehicle or F2A (0.3, 1.0, or 3.0 mg/kg) daily for 14 days. Histomorphometric analyses were performed in the proximal tibial metaphyses. Hematocrit was normal in F2A-treated OVX rats. Although organ function was not evaluated, histological examination of several organs did not detect any abnormalities. F2A treatment did not increase cancellous bone mass regardless of dose, but OVX rats treated with 1 mg/kg did exhibit increased osteoclast surface. All 3 doses of F2A induced a modest increase in cancellous bone formation. Therefore, F2A appears to increase both cancellous bone resorption and formation, but these skeletal processes are in balance so that, unlike FGF-2, cancellous bone mass is not augmented. However, F2A did not induce the anemia and impaired bone mineralization associated with FGF-2. Therefore, local application of F2A for orthopedic procedures would presumably have minimal side effects, even if the peptide is released to the systemic circulation.

Interaction of Tritrichomonas foetus with the reproductive tract of experimentally infected female BALB/c mice: Ultrastructural evaluation

The interaction of Tritrichomonas foetus with its host is a complex process that involves colonisation, attachment and persistence. The goal of the present study was to describe the interaction of T. foetus with the genital tract using a model of non-oestrogenised female BALB/c mice which had been intravaginally infected with a suspension of T. foetus during oestrus. Animals were sacrificed after 10 weeks and the uteri fixed and processed for light and electron microscopy. Ultrastructural analysis showed that the attached protozoa interacted with the mucosa through a somal projection. With an amorphous secretion at the protozoa-host cell interface. There was no direct contact between the protozoal plasma membrane and the epithelial cell membrane. Our results demonstrated the participation of an active phagocytosis and the destruction of T. foetus by eosinophils.

Mechanical stimulation prevents osteocyte apoptosis: requirement of integrins, Src kinases, and ERKs

Osteocytes, former osteoblasts entombed in the bone matrix, form an extensive cell communication network that is thought to detect microdamage and mechanical strains and to transmit signals leading to repair and compensatory bone augmentation or reduction. Bone active hormones and drugs control the integrity of this network by regulating osteocyte apoptosis, which might be a determinant of bone strength. Herein we demonstrate that mechanical stimulation by stretching activates the ERKs, which in turn are responsible for the attenuation of osteocyte apoptosis. The effect of osteocyte stretching is transmitted by integrins and cytoskeletal and catalytic molecules, such as Src kinases. Stretch-induced antiapoptosis also requires nuclear translocation of ERKs and new gene transcription. The evidence linking mechanical stimulation, activation of an integrin/cytoskeleton/Src/ERK signaling pathway, and osteocyte survival provides a mechanistic basis for the profound role of mechanical forces, or lack thereof, on skeletal health and disease.

Vascular remodeling and ET-1 expression in rat strains with different responses to chronic hypoxia

Chronic hypoxia leads to a greater degree of pulmonary hypertension in the Wistar-Kyoto (WKY) rat than in the Fischer 344 (F-344) rat. We questioned whether this difference is associated with baseline differences in pulmonary artery anatomy, a greater degree of hypoxia-induced pulmonary vascular remodeling in the WKY rat, and/or differences in expression of endothelin (ET)-1. Male F-344 and WKY rats were maintained in normoxia or normobaric hypoxia for 21 days. Morphometry revealed that baseline pulmonary artery anatomy was similar in the two strains. However, during chronic hypoxia, the WKY rats developed a greater degree of muscularization of small pulmonary arteries. Baseline plasma and lung immunoreactive ET-1 levels were similar in the WKY and F-344 rats and increased significantly during hypoxia in the WKY rats. Northern analysis demonstrated increased lung preproET-1 mRNA during hypoxia in both strains, with a greater increase in WKY rats. Immunostaining demonstrated increased ET-1 in bronchial epithelium and peripheral pulmonary arteries during hypoxia, although to a greater degree in the WKY rats. We conclude that the WKY strain demonstrates increased susceptibility to hypoxia-induced pulmonary vascular remodeling compared with the F-344 strain and that increased lung and circulating ET-1 levels during hypoxia may partly explain this difference.

Lectin histochemical study on the kidney of normal and streptozotocin-induced diabetic hamsters

Lectin histochemical characteristics of the kidney of normal and streptozotocin (SZ)-induced diabetic APA hamsters were investigated. Paraffin sections of the kidney of animals killed at 1 and 3 months after SZ-injection were stained with the following 10 lectins: PNA, BPA, DBA, SBA, GSA-I, GSA-II, MPA, WGA, UEA-1 and Con A. Renal lectin binding characteristics of normal APA hamsters differed in some aspects from those in other species reported previously. In the kidney of SZ-induced diabetic APA hamsters, binding activities of some lectins increased in the affected Bowman's capsules and glomeruli as well as in degenerated epithelial cells of uriniferous tubules. Among them, GSA-II in particular exhibited strong binding activity to the degenerated epithelial cells of Bowman's capsules, distal convoluted tubules and collecting ducts.