Testosterone Regulates Bone Response to Inflammation

Abstract

This study evaluated the alveolar bone response to testosterone and the impact of Resolvin D2 (RvD2) on testosterone-induced osteoblast function. For the in vivo characterization, 60 male adult rats were used. Treatments established sub-physiologic (L), normal (N), or supra-physiologic (H) concentrations of testosterone. Forty rats were subjected to orchiectomy; 20 rats received periodical testosterone injections while 20 rats received testicular sham-operation. Four weeks after the surgeries, 10 rats in each group received a subgingival ligature around the lower first molars to induce experimental periodontal inflammation and bone loss. In parallel, osteoblasts were differentiated from neonatal mice calvariae and treated with various doses of testosterone for 48 h. Cell lysates and conditioned media were used for the determination of alkaline phosphatase, osteocalcin, RANKL, and osteoprotegerin. Micro-computed tomography linear analysis demonstrated that bone loss was significantly increased for both L and H groups compared to animals with normal levels of testosterone. Gingival IL-1β expression was increased in the L group (p < 0.05). Ten nM testosterone significantly decreased osteocalcin, RANKL, and OPG levels in osteoblasts; 100 nM significantly increased the RANKL:OPG ratio. RvD2 partially reversed the impact of 10 nM testosterone on osteocalcin, RANKL, and OPG. These findings suggest that both L and H testosterone levels increase inflammatory bone loss in male rats. While low testosterone predominantly increases the inflammatory response, high testosterone promotes a higher osteoblast-derived RANKL:OPG ratio. The proresolving mediator RvD2 ameliorates testosterone-derived downregulation of osteocalcin, RANKL, and OPG in primary murine osteoblasts suggesting a direct role of inflammation in osteoblast function.

The effects of orchidectomy and supraphysiological testosterone administration on trabecular bone structure and gene expression in rats

“…The expression of RANKL and OPG genes decreased significantly in the TE group. Previous studies had reported decreased RANKL and OPG levels with testosterone treatment [26,27]. However, the decrease in RANKL gene expression was not accompanied by a decrease in osteoclastic gene expression in this study.…”

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

“…Many in vitro studies assess the role of androgens on different periodontal soft tissue cells: in gingival connective tissue testosterone inhibits prostaglandin formation [26], in inflamed gingiva androgens increase 5-alpha-reductase activity [27]; and in fibroblasts, increasing concentrations of androgens inhibit IL-6 production [28, 29] and increase cell proliferation [30]. Previous studies have demonstrated that low and high testosterone levels in rats increase both gingival and connective tissue areas [13], increase periodontal bone loss; and impact the release of RANKL and osteoprotegerin by murine osteoblasts [14]. …”

“…The histogram settings were standardized at 90–130 and 101 serial slices were selected in each sample. Bone volume fraction was analyzed by the CT-scan software [14]. …”

“…Research suggests that testosterone may impact bone tissues and cells [10–14]. Testosterone can act directly, through binding to the androgen receptor, or indirectly, by its conversion to a more potent hormone, DHT.…”

“…This overproduction leads to tissue breakdown and the consequent resorption of the alveolar process, a bone structure consisting of outer cortical plates of compact bone, a central spongiosa (trabecular bone), and bone lining the alveolus (alveolar bone) [21]. Our previous studies suggest that both low and high testosterone levels regulate experimental bone loss in rats [13, 14]. This study tests the hypothesis that testosterone suppression increases inflammation-induced bone loss through the reduction of androgen receptor activation.…”