Metabolic, Endocrine, and Central Effects of Genistein Aglycone in Glucocorticoid Induced Osteoporosis

Glucocorticoid-induced osteoporosis (GIOP) is one of the primary side effects of glucocorticoid use resulting in increased risk of fractures. Glucocorticoid therapy affects bone mass, glucidic and lipidic metabolism, thyroid function and is also responsible for a decline in cognitive function. In this study a natural approach will be used, a soy-derived isoflavone, namely genistein. Genistein has been proven effective in preserving bone mineral density in post-menopausal women, and has an high safety profile. Genistein was also able in improving cardiovascular markers, as well as lipidic and glucidic metabolism markers without interfering with thyroid function.

Treatment guidelines for the use of glucocorticoids have been established which advise that if prednisolone is administered at 5 mg per day for three months or longer requires regular monitoring of bone mineral density (BMD) and treatment to prevent osteoporosis must be initiated (American college of Rheumatology). Vitamin D and calcium are also recommended for the management of all patients treated with glucocorticoids. Bisphosphonates should be considered for the prevention and treatment of this disorder, because they can prevent the initial loss of bone mass from glucocorticoids. Alendronate, risedronate, and zoledronic acid were shown to prevent and reverse the loss of BMD in glucocorticoid-induced osteoporosis with greater effects than those observed with vitamin D and calcium. In fact, bisphosphonates induce improvement of BMD that is 2-fold greater than that observed during vitamin D treatment alone (4.6% vs. 2.0%, respectively). Anabolic therapy is also used for the treatment of glucocorticoid-induced osteoporosis. Teriparatide causes a greater increase in BMD than alendronate and greater reduction in the risk of vertebral fractures. Even with these evidentiary clinical trials and guidelines, patient bone loss is, in general, poorly managed. In glucocorticoid-induced osteoporosis, fractures also occur at higher BMDs than in postmenopausal osteoporosis in untreated women. Consequently, guidelines for the treatment of postmenopausal osteoporosis are not applicable to glucocorticoid-induced osteoporosis, and patients should be treated at BMD T-scores of -1.0 to -1.5 standard deviations. In addition, vertebral fractures may be asymptomatic and often require radiological diagnosis before treatment.

During the initial phases of glucocorticoid exposure bone resorption is increased. Glucocorticoids inhibit the formation of mature osteoblasts, but also activate an activate apoptosis in these cell types. Osteoprotegrin (OPG) expression, a key factor involved in modulating maturation of osteoclasts, is reduced also by glucocorticoids resulting in increased osteoclastogenesis. Therefore, the combination of reduced osteoblast formation, increased osteoclast maturation leads to accelerated bone loss while on glucocorticoid therapy. Therapies are needed which modulate osteoclast as well as osteoblast activity to restore a more normal balance to the bone remodeling process in glucocorticoid treated patients.

A rational treatment for glucocorticoid-induced osteoporosis should combine a significant anti-osteoporotic and anti-fracture activity with positive actions on the several undesirable effects of this therapy including alteration in glucose and lipid metabolism, amplification of the cardiovascular risk, impairment in thyroid and cognitive function.

Genistein aglycone represents an innovative therapeutic bullet to challenge the metabolic derangements induced by glucocorticoids. Among the anabolic compounds tested in recent years genistein aglycone seems a promising agent able to stimulate bone formation and to reduce bone resorption, acting via a genomic as well as a non-genomic pathways. Genistein is an isoflavone found in small quantities in certain legumes throughout the plant kingdom. Genistein has both ER agonist and antagonist activity in different cell types and works in a promoter specific manner in gene activation via ERs. Effects of genistein on bone metabolism derived from direct and indirect actions on bone cells and can be summarized in stimulation of osteoblastic bone formation and inhibition of osteoclastic bone resorption.