Effect of alendronate on the mandible and long bones: an experimental study in vivo

Lactobacillus plantarum attenuates glucocorticoid-induced osteoporosis by altering the composition of rat gut microbiota and serum metabolic profile

Introduction

Osteoporosis, one of the most common non-communicable human diseases worldwide, is one of the most prevalent disease of the adult skeleton. Glucocorticoid-induced osteoporosis(GIOP) is the foremost form of secondary osteoporosis, extensively researched due to its prevalence.Probiotics constitute a primary bioactive component within numerous foods, offering promise as a potential biological intervention for preventing and treating osteoporosis. This study aimed to evaluate the beneficial effects of the probiotic Lactobacillus plantarum on bone health and its underlying mechanisms in a rat model of glucocorticoid dexamethasone-induced osteoporosis, using the osteoporosis treatment drug alendronate as a reference.

Methods

We examined the bone microstructure (Micro-CT and HE staining) and analyzed the gut microbiome and serum metabolome in rats.

Results and discussion

The results revealed that L. plantarum treatment significantly restored parameters of bone microstructure, with elevated bone density, increased number and thickness of trabeculae, and decreased Tb.Sp. Gut microbiota sequencing results showed that probiotic treatment increased gut microbial diversity and the ratio of Firmicutes to Bacteroidota decreased. Beneficial bacteria abundance was significantly increased (Lachnospiraceae_NK4A136_group, Ruminococcus, UCG_005, Romboutsia, and Christensenellaceae_R_7_group), and harmful bacteria abundance was significantly decreased (Desulfovibrionaceae). According to the results of serum metabolomics, significant changes in serum metabolites occurred in different groups. These differential metabolites were predominantly enriched within the pathways of Pentose and Glucuronate Interconversions, as well as Propanoate Metabolism. Furthermore, treatment of L. plantarum significantly increased serum levels of Pyrazine and gamma-Glutamylcysteine, which were associated with inhibition of osteoclast formation and promoting osteoblast formation. Lactobacillus plantarum can protect rats from DEX-induced GIOP by mediating the "gut microbial-bone axis" promoting the production of beneficial bacteria and metabolites. Therefore L. plantarum is a potential candidate for the treatment of GIOP.

Alendronate induces skeletal alterations in the chicken embryonic development model

Alendronate, a nitrogen-containing bisphosphonate, has reported long-term clinical success in the management of distinct bone-related conditions, particularly in the modulation of post-menopausal osteoporosis. Nonetheless, whether the inhibitory activity over osteoclastic cells' functionality is widely acknowledged, contradictory evidence arises from the assessment of alendronate activity over osteoblastic populations. This may be of particular relevance in situations in which bone formation exceeds bone resorption, with further emphasis on embryonic development, since alendronate can cross the placental barrier and alendronate-based therapies are being extended into women of reproductive age. Accordingly, the present study aims to assess the effects of alendronate, at distinct concentrations (1.5E-10M to 1.5E-7M) on bone tissue development, within a translational animal model - the embryonic chicken development model. Embryos, at the beginning of osteogenesis (day 7) were exposed to different alendronate concentrations for 4 days. Embryos were following characterized for skeletal development by histomorphometric analysis upon histochemical staining, microtomographic analysis, and gene expression assessment of genes related to osteoclastogenic/osteoclastic and osteoblastogenic/osteogenic differentiation, as well as to the immuno-inflammatory activation. The findings revealed that exposure to alendronate had a dose-dependent impact on skeletal growth and mineralization. This effect was evidenced by diminished bone volume and reduced bone surface parameters, with the 1.5E-7M concentration leading to a remarkable reduction of over 50%. Additionally, a decreased osteoclastogenic/osteoclastic gene expression was verified, associated with a diminished osteoblastogenic/osteogenic program - within the 30-50% range for 1.5E-7 M, supporting the diminished bone formation process. An increased inflammatory activation may contribute, at least in part, to the attained outcomes. Overall present findings suggest a negative influence of alendronate on the embryonic bone development process in a dose-dependent manner, highlighting the potential risk of alendronate use during embryonic development.

Dentists' knowledge about osteoporosis and their ability to identify the disease

BACKGROUND

Osteoporosis is an underdiagnosed condition, and its seriousness is not considered until severe complications arise. This study aimed to evaluate general dentists' knowledge about osteoporosis and their ability to identify patients with this disease by assessing mandibular cortical width (MCW) and mandibular cortical index (MCI) on panoramic dental radiographs using a visual method.

METHODS

In this cross-sectional study, an email questionnaire regarding the diagnosis and prevention of osteoporosis was sent to 20,773 dentists in 2016. Those who completed the questionnaire were invited to participate in radiomorphometric training and then to analyze the MCI and MCW of 114 panoramic radiographs of postmenopausal women who underwent both panoramic radiography and bone densitometry. Based on the radiomorphometric indices and while blinded to the densitometry results, the dentists determined whether they would indicate densitometry for these patients.

RESULTS

The response rate was 2.3%: 485 dentists completed the questionnaire, and 50 evaluated panoramic radiographs using the MCW and MCI. All of them reported some knowledge about osteoporosis, but 41.6% demonstrated a misleading conceptualization of the disease. Approximately 90% reported minimal access to this information during graduation, and only 27.0% were exposed to the topic during their postgraduate studies. Interest in osteoporosis prevention was expressed by 70.7% of the respondents, and interest in learning the radiomorphometric indices was expressed by 99.0%. The sensitivity in the detection of low bone mineral density through the MCW and MCI was 52.9%, and the specificity was 64%.

CONCLUSIONS

Brazilian dentists demonstrated insufficient knowledge about osteoporosis and a low ability to detect osteopenia or osteoporosis by applying radiomorphometric indices.

Intermittent hypoxia inhibits mandibular cartilage growth with reduced TGF-β and SOX9 expressions in neonatal rats

Intermittent hypoxia (IH) has been associated with skeletal growth. However, the influence of IH on cartilage growth and metabolism is unknown. We compared the effects of IH on chondrocyte proliferation and maturation in the mandibular condyle fibrocartilage and tibial hyaline cartilage of 1-week-old male Sprague-Dawley rats. The rats were exposed to normoxic air (n = 9) or IH at 20 cycles/h (nadir, 4% O₂; peak, 21% O₂; 0% CO₂) (n = 9) for 8 h each day. IH impeded body weight gain, but not tibial elongation. IH also increased cancellous bone mineral and volumetric bone mineral densities in the mandibular condylar head. The mandibular condylar became thinner, but the tibial cartilage did not. IH reduced maturative and increased hypertrophic chondrocytic layers of the middle and posterior mandibular cartilage. PCR showed that IH shifted proliferation and maturation in mandibular condyle fibrocartilage toward hypertrophic differentiation and ossification by downregulating TGF-β and SOX9, and upregulating collagen X. These effects were absent in the tibial growth plate hyaline cartilage. Our results showed that neonatal rats exposed to IH displayed underdeveloped mandibular ramus/condyles, while suppression of chondrogenesis marker expression was detected in the growth-restricted condylar cartilage.

Imaging and histomorphometric evaluation of mandible and tibia of rats treated with bisphosphonates

OBJECTIVES

To evaluate the mandible and tibia of rats treated with bisphosphonates (BPs) by imaging and histomorphometric analysis.

STUDY DESIGN

Thirty-four rat specimens (Rattus norvegicus, Wistar strain) were distributed into 3 groups: (1) 12 rats treated with zoledronic acid; (2) 12 rats treated with clodronate; and (3) the control group, containing 10 rats that received saline. All bones were exposed to cone beam computed tomography (CBCT). The images were analyzed to determine bone density (BD), using the software OsiriX 7.0. Histological slides were prepared from the specimens and the proportion of bone volume (BV) was quantified using the software Adobe Photoshop CC.

RESULTS

There was no statistically significant difference in BD either between the drug groups or between mandible and tibia. BV between BPs and control group did not show a significant difference. However, comparing the two bones, the mandibles in the control group displayed higher BV than did the tibiae in the same group.

CONCLUSION

According to our results, we conclude that (1) BD was not altered by bone type or by type of BP administered, and (2) treatment with zoledronic acid or clodronate did not affect BV in the mandible or tibia of test groups.

Indirect osteoblast differentiation by liposomal clodronate

Bisphosphonates impair function of osteoclasts and prevent bone resorption, the mechanism of which has been studied extensively. However, the possible effects of bisphosphonates on chondroblast differentiation and calcium deposition by osteoblasts have only been demonstrated recently. Moreover, cells from monocytic lineage are capable of stimulating osteoblast proliferation. Hence, susceptibility of osteoblasts to various factors requires further investigation. A primary culture of bone marrow‐derived stromal cells was treated with liposomal clodronate (0.1, 0.5, or 1.0 mg/ml) or conditioned medium from liposomal clodronate. Liposomal clodronate (0.25 mg) was injected into mouse femur for in vivo experiments. The effects of liposomal clodronate were examined by alkaline phosphatase staining and/or activity assay, and real‐time RT‐PCR was used for studying the effect on osteogenic gene expression. Administration of liposomal clodronate to bone marrow‐derived mesenchymal stromal cell culture enhanced alkaline phosphatase activity and mRNA levels of Runx2 and Dlx5. In addition, conditioned medium from liposomal clodronate also stimulated osteogenic characteristics similar to those of observed in vitro, and the number of exosomes in the conditioned medium was highest when pre‐treated with liposomal clodronate. Western blot analysis revealed the presence of RANK proteins in exosomes collected from conditioned medium of liposomal clodronate. Identical observations were obtained in vivo, as liposomal clodronate‐injected mouse femur showed increased alkaline phosphatase activity and Runx2 and Dlx5 mRNA expressions, even though the numbers of monocytes and macrophages were reduced. In conclusion, osteoblast differentiation was promoted via soluble RANK‐containing exosomes in response to clodronates.

Neural crest-mediated bone resorption is a determinant of species-specific jaw length

Precise control of jaw length during development is crucial for proper form and function. Previously we have shown that in birds, neural crest mesenchyme (NCM) confers species-specific size and shape to the beak by regulating molecular and histological programs for the induction and deposition of cartilage and bone. Here we reveal that a hitherto unrecognized but similarly essential mechanism for establishing jaw length is the ability of NCM to mediate bone resorption. Osteoclasts are considered the predominant cells that resorb bone, although osteocytes have also been shown to participate in this process. In adults, bone resorption is tightly coupled to bone deposition as a means to maintain skeletal homeostasis. Yet, the role and regulation of bone resorption during growth of the embryonic skeleton have remained relatively unexplored. We compare jaw development in short-beaked quail versus long-billed duck and find that quail have substantially higher levels of enzymes expressed by bone-resorbing cells including tartrate-resistant acid phosphatase (TRAP), Matrix metalloproteinase 13 (Mmp13), and Mmp9. Then, we transplant NCM destined to form the jaw skeleton from quail to duck and generate chimeras in which osteocytes arise from quail donor NCM and osteoclasts come exclusively from the duck host. Chimeras develop quail-like jaw skeletons coincident with dramatically elevated expression of TRAP, Mmp13, and Mmp9. To test for a link between bone resorption and jaw length, we block resorption using a bisphosphonate, osteoprotegerin protein, or an MMP13 inhibitor, and this significantly lengthens the jaw. Conversely, activating resorption with RANKL protein shortens the jaw. Finally, we find that higher resorption in quail presages their relatively lower adult jaw bone mineral density (BMD) and that BMD is also NCM-mediated. Thus, our experiments suggest that NCM not only controls bone resorption by its own derivatives but also modulates the activity of mesoderm-derived osteoclasts, and in so doing enlists bone resorption as a key patterning mechanism underlying the functional morphology and evolution of the jaw.