Bone and Men's Health. Effects of aromatase inhibitors on human osteoblasts

Aromatase inhibitors (AIs) have been widely employed as an adjuvant endocrine therapy in postmenopausal patients with estrogen receptor (ER) positive breast carcinoma in place of tamoxifen. AIs work on suppressing both systemic and local estrogen biosynthesis in an almost complete manner resulting in estrogen depletion and subsequently inhibition of estrogen dependent carcinoma cell proliferation. Despite marked therapeutic effects in these patients, potential side effects related to long term and marked estrogen depletion should be considered for the benefits of these patients. Among these possible side effects, bone loss and/or increased rates of pathological fractures may be considered one of the most serious complications in terms of effecting activities of daily life of the patients. AIs can be classified into two types, steroidal and non-steroidal in terms of their structure and modes of actions. The former is also characterized to display androgenic actions. Estrogens are well-known to exert their effects primarily through osteoblasts in human bone tissues. Therefore, in this review, we will summarize in vitro effects of AIs, especially androgenic effects of steroidal AIs upon human osteoblasts in order to further understand their effects on human skeletal systems.