Strontium ranelate promotes increased peri-implant bone formation in ovariectomized

This study aimed to evaluate the systemic effect of strontium ranelate (SR) on peri-implant bone tissue. Thirty-six adult rats were divided into three experimental groups: sham (SHAM), ovariectomized (OVX) and ovariectomized rats treated with strontium ranelate (OVX-Sr). Strontium ranelate (625mg/kg) was administered by oral gavage on a daily basis. The implants were installed on the tibiae. The euthanasia occurred 42 and 60 days after the implants were installed, and the biomechanical (reverse torque); PCR-RT; histological; immunohistochemical; confocal microscopy and histometric analysis were performed. Quantitative data was subjected to statistical tests with significance level set at p<0.05. Significant increase in implant reverse torque in OVX-Sr was observed when compared to OVX. PCR analysis showed an increase in the genetic expression of the proteins responsible for bone formation in OVX-SR. In the histological analysis, SHAM and OVX-Sr showed a higher degree of maturation of peri-implant bone tissue. Ran-Sr presented higher immunolabeling for ALP and OPN proteins when compared to OVX. In the confocal microscopy, OVX-Sr there was good bone neoformation showed by incorporation of Alizarin red fluorochrome. The histometric analysis, bone implant contact (BIC) and neoformed bone area (NBA) presented statistically difference among all groups, and the Ran-Sr presented the highest BIC. Thus, strontium ranelate improves osseointegration and quality of neoformed bone tissue around implants in estrogen deficient rats. histológico, SHAM y OVX-Sr mostraron un mayor grado de maduración del tejido óseo periimplantario. OVX-Sr mostró una marca de inmunidad más alta para las proteínas ALP y OPN en comparación con OVX. En la microscopía confocal, OVX-Sr hubo una buena neoformación ósea mostrada por la incorporación del fluorocromo rojo de Alizarin. El análisis histórico, el contacto con el implante óseo (BIC) y el área ósea neoformada (NBA) mostraron diferencias estadísticas entre todos los grupos, y Ran-Sr mostró el BIC más alto. Así, el ranelato de estroncio mejora la osteointegración y la calidad del tejido óseo neoformado alrededor de los implantes en ratas con deficiencia de estrógeno.


Molecular Analysis (PCR)
Relative gene expression for ALP, the enzyme that induces phosphate precipitation over bone matrix, was significantly higher in OVX-SR compared to the other groups (P<0.0001).
For non-collagen protein OCN, which signals bone mineralization, presented higher values of relative gene expression in OVX-SR compared to SHAM and OVX groups (P<0.0001).
Regarding OPG and RANKL proteins, the OVX-SR group presented the highest expression for OPG and the lowest expression for RANKL among the studied groups (Graphic 2). Research, Society and Development, v. 9, n. 10, e7539109092, 2020 (CC BY 4.

Morphometric Analysis
Histological analysis shows that the peri-implant repair in the SHAM showed a greater degree of corticalization in the osseointegration area in all corresponding spaces around the implants, with formation of mature bone tissue. In the OVX, there was formation of new bone with corticalization only in the first implants thread, and in the more superficial portions. In the medullary portion, small area of bone formation was observed in contrast to the large amount of adipose tissue observed in this region. In the OVX-Sr, an improvement in the maturation of peri-implant bone tissue was observed with histological images very close to those of the SHAM. Research, Society and Development, v. 9, n. 10, e7539109092, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.9092

Immunolabeling Analysis
Immunolabels were evaluated in the region of bone tissue formed next to the implants, to characterize the different cell stages of the osteoblastic lineage, was observed the presence of the RUNX2, positive in pre-osteoblasts and osteoblasts. The ALP labeling the activity of alkaline phosphate precipitation on the organic matrix of type I collagen. OPN, positive for cells of the osteoblastic lineage and shows the calcium precipitation activity on the organic matrix based on type I collagen, and OCN, labels mature osteoblasts at the end of the mineralization phase of calcium on the organic matrix of collagen.
RUNX2 was positively showed in all experimental groups. SHAM and OVX-Sr groups showed moderate labeling. OVX presented an intense labeling, however it occurred in the non-mineralized tissue.
Intense labeling for ALP was observed in the SHAM. In the OVX, a light labeling was observed. After treatment with Ran-Sr, moderate staining was observed for ALP in osteoblasts present in the bone tissue.
In SHAM and OVX-Sr, moderate labeling for OPN was showed, especially for endosteal cells. In the OVX, discrete labeling was observed in connective tissue.
In the SHAM, the OCN showed moderate labeling in osteocytes in the bone tissue formed around to the implants. In OVX, light labeling was observed for OCN in cells similar Development, v. 9, n. 10, e7539109092, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.9092 14 to osteoblasts without mineralization characteristics. The OVX-Sr presented bone tissue around the implant with a light labeling for OCN in the osteocytes of this region.

Microtomographic analysis
There were no significant differences between groups for the parameters evaluated in microtomography (Graphic 3).