Bone action of the phytoestrogen genistein under hypoestrogenism and obesity

Osteoporosis and obesity are prevalent diseases in menopause. The phytoestrogen genistein (Gen) is an antioxidant/anti-inflammatory agent proposed as natural therapy to counteract syndromes associated to menopause. In this work we evaluated the bone effect of Gen in a stress environment induced by hypoestrogenism and obesity. Bilaterally ovariectomized female Wistar rats were fed with high-fat diet (obese), or standard diet (non-obese). Osteoblasts (OB) primary cultures from femoral shafts, and retroperitoneal explants of white adipose tissue (WAT) in vitro exposed to Gen were employed as experimental systems. In obese rats, bone oxidative stress revealed by enhancement on H₂O₂ release, and significant reduction in OB nitric oxide (NO) production, cell growth, alkaline phosphatase activity (ALP), matrix mineralization and collagen deposition was detected. In OB-WAT co-cultures, Gen treatment inhibited H₂O₂ secretion, and prompted OB differentiation. A direct action of Gen on WAT was demonstrated. The phytoestrogen inhibited H₂O₂ and TBARS production, and diminished the secretion of the inflammatory adipokine leptin, through a mechanism of action mediated by estrogen receptor (ER) involvement, and MAPK and PI3K signal transduction pathways participation. A directional interaction from WAT to bone was evidenced by the incubation OB with conditioned medium obtained from WAT exposed to Gen (Gen-CM). The presence of Gen-CM improved OB growth, and reduced H₂O₂ production. The antioxidative effect of Gen on obese bone cells was partially dependent on its ability to reduce leptin secretion by WAT. Altogether, the results suggest that, under obesity, Gen may improve bone metabolism through a direct action on WAT.