Neonatal rat osteoblasts bioconvert testosterone to non-phenolic metabolites with estrogen-like effects on bone cell proliferation and differentiation

Abstract

Testosterone (T) restores bone mass loss in postmenopausal women and osteoporotic men mainly through its bioconversion to estradiol (E2). In target tissues, T is also biotransformed to the A-ring-reduced metabolites 3α,5α-androstanediol (3α,5α-diol) and 3β,5α-androstanediol (3β,5α-diol), which are potent estrogen receptor (ER) agonists; however, their biological role in bone has not been completely elucidated. To assess if osteoblasts bioconvert T to 3α,5α-diol and to 3β,5α-diol, we studied in cultured neonatal rat osteoblasts the metabolism of [14C]-labeled T. In addition, the intrinsic estrogenic potency of diols on cell proliferation and differentiation in neonatal calvarial rat osteoblasts was also investigated. Osteoblast function was assessed by determining cell DNA, cell-associated osteocalcin, and calcium content, as well as alkaline phosphatase activity and Alp1 gene expression. The results demonstrated that diols were the major bioconversion products of T, with dihydrotestosterone being an obligatory intermediary, thus demonstrating in the rat osteoblasts the activities of 5α-steroid reductase and 3α- and 3β-hydroxysteroid dehydrogenases. The most important finding was that 3β,5α- and 3α,5α-diols induced osteoblast proliferation and differentiation, mimicking the effect of E2. The observation that osteoblast differentiation induced by diols was abolished by the presence of the antiestrogen ICI 182,780, but not by the antiandrogen 2-hydroxyflutamide, suggests that diols effects are mediated through an ER mechanism. The osteoblast capability to bioconvert T into diols with intrinsic estrogen-like potency offers new insights to understand the mechanism of action of T on bone cells and provides new avenues for hormone replacement therapy to maintain bone mass density.

Intracrine Regulation of Estrogen and Other Sex Steroid Levels in Endometrium and Non-gynecological Tissues; Pathology, Physiology, and Drug Discovery

“…Since both E1-S and DHEA-S elicit effects similar to E2, which are blocked by STS inhibition (Selcer and Difrancesca, 2012 ; Dias and Selcer, 2014 ), these studies demonstrate that conjugated steroids are activated and that DHEA is converted to E2. Studies in rat osteoblast with [14C]T demonstrated that T is converted by SRD5As and AKR1Cs to 3α/3βDIOLs, which induce proliferation via activation of ER (and not AR) (Enríquez et al, 2013 ).…”

Actividad enzimática de las células MCF-7 de cáncer de mama para biotransformar gestodeno a metabolitos no fenólicos capaces de inducir la proliferación celular

“…La pronta (15 min) y abundante formación del metabolito 5α-GSD, seguida de un descenso muy marcado a través de los subsecuentes tiempos de incubación y, en forma concomitante, el incremento en la formación de 3β,5αGSD y de su epímero 3α, aunque en menor proporción, es acorde con el concepto de que en esteroides naturales como la testosterona, la molécula 5α-reducida es un intermediario obligatorio en la biosíntesis de los tetrahidros 3α y 3β (Pérez- Enríquez et al, 2013). De acuerdo a los resultados obtenidos, en la Figura 8 se representa el destino metabólico de la molécula de GSD en las células MCF-7 de cáncer de mama.…”