Androgen receptors and experimental bone loss — an in vivo and in vitro study

Abstract

Testosterone is a sex hormone that exhibits many functions beyond reproduction; one such function is the regulation of bone metabolism. The role played by androgen receptors during testosterone-mediated biological processes associated with bone metabolism is largely unknown. This study aims to use a periodontal disease model in vivo in order to assess the involvement of androgen receptors on microbial-induced inflammation and alveolar bone resorption in experimental bone loss. The impact of hormone deprivation was tested through both orchiectomy and chemical blockage of androgen receptor using flutamide (FLU). Additionally, the direct effect of exogenous testosterone, and the role of the androgen receptor, on osteoclastogenesis were investigated. Thirty male adult rats (n=10/group) were subjected to: 1- orchiectomy (OCX); 2- OCX sham-surgery; or 3- OCX sham-surgery plus FLU, four weeks before the induction of experimental bone loss. Ten OCX sham-operated rats were not subjected to experimental bone loss and served as healthy controls. The rats were euthanized two weeks later, so as to assess bone resorption and the production of inflammatory cytokines in the gingival tissue and serum. In order to study the in vitro impact of testosterone, osteoclasts were differentiated from RAW264.7 cells and testosterone was added at increasing concentrations. Both OCX and FLU increased bone resorption, but OCX alone was observed to increase osteoclast count. IL-1β production was increased only in the gingival tissue of OCX animals, whereas FLU-treated animals presented a decreased expression of IL-6. Testosterone reduced the osteoclast formation in a dose-dependent manner, and significantly impacted the production of TNF-α; FLU partially reversed these actions. When taken together, our results indicate that testosterone modulates experimental bone loss, and that this action is mediated, at least in part, via the androgen receptor.

The role of androgens on periodontal repair in female rats

“…Due to the conversion of testosterone in estradiol, we used a pharmacologic model of androgen receptor blockade (administering flutamide) to compare the results with the orchiectomy model, thus isolating the impact of androgens on bone, obtaining similar clinical results. In vitro , we demonstrated that physiologic testosterone levels (10 nM), but not low or high levels, are able to downregulate osteoclastogenesis both directly and indirectly, decreasing murine osteoblasts‐derived RANKL expression . Using data from the III National Health and Nutrition Examination Survey, we showed a positive association between high total TES and bioavailable testosterone and the presence and severity of periodontitis …”

“…Low testosterone levels have been extensively related with a number of clinical alterations of normality, including libido and sexual function loss, muscular strength loss, fatigue, cognitive and mood alterations, as well as an increase in cardiovascular disease markers, mortality, diabetes mellitus, metabolic syndrome and increased risk for bone fracture . Our group has demonstrated that not only low levels of testosterone, as those obtained after orchiectomy, increase ligature‐induced periodontal bone loss in rats, but also supraphysiologic levels of the hormone . Due to the conversion of testosterone in estradiol, we used a pharmacologic model of androgen receptor blockade (administering flutamide) to compare the results with the orchiectomy model, thus isolating the impact of androgens on bone, obtaining similar clinical results.…”

“…The structure in each intersection was recorded as ‘inflammatory cell’, ‘other structure’ or ‘out of the region of interest’. For the percentage of inflammatory cells, all ‘out of the region of interest’ intersection points were discarded and the remaining points were considered to be 100% …”

“…Our previous findings suggested that androgens play an important role on periodontal disease progression in male rats by affecting connective and epithelial tissues, as well as alveolar bone . We hypothesized that androgens also play a role on bone and soft tissue metabolism during repair in females.…”

Long‐term testosterone depletion attenuates inflammatory bone resorption in the ligature‐induced periodontal disease model

“…Our research group has shown the complexity of biological responses associated with both decrease and increase of testosterone levels in the experimental periodontal disease model . Short‐term reduction of testosterone levels in young animals caused an increase of inflammatory bone resorption and osteoclast numbers with a corresponding increase in locally‐produced IL‐1β in vivo; whereas in vitro testosterone suppressed RANKL‐induced osteoclastogenesis .…”