In general cellular senescence is considered a
In general, cellular senescence is considered a programmed response to stress that can be activated by oxidative stress, irradiation or action of substances or drugs. These stressors cause DNA damage and, through the action of specific proteins (p53 and p21), lead to cell senescence (di Fagagna, 2008). Assays that evaluate DNA damage as a cause of senescence are usually carried out in a short time, within 24h, considering that in longer periods repair mechanisms can be activated. For that reason, this experiment was performed at 6 and 12h, differing from other treatment times (48h) used in the present study. Thus, DNA damage appears to be a key aspect that would justify the presence of senescence in cells supplemented with Leu. The potential toxic effect of Leu and its relation to DNA damage has mainly been studied in pathological situations in which this amino Phos-tag Biotin is not metabolized properly and ends up accumulating in the body, as in the case of patients with maple syrup urine disease (MSUD) (Strauss et al., 2013). Studies in vitro under conditions that mimic toxic environment by excessive Leu, as well as in individuals with MSUD, show that excess of Leu may cause cellular damage increased by DNA rupture (Mescka et al., 2015). This damage can occur even in cells from healthy individuals (Mescka et al., 2014). Our results indicate that Leu also has a potential toxic effect on MC3T3-E1 cells, since its 12.5% increase, as compared to the levels that are considered optimal for the culture medium of these cells, was able to promote DNA damage and, consequently, cellular senescence at 6 and 12h of treatment.
Introduction Osteoporosis is a progressive bone disease that is characterized by reduced bone mass and disruption of bone architecture, which can lead to an increased risk of fragility fracture . As society ages, increasing numbers of patients with osteoporosis and osteoporotic fractures have a serious economic impact on society . During the past three decades, a variety of medications have been used for the prevention and treatment of osteoporosis, but few are entirely satisfactory. For example, bisphosphonates are popular drugs that effectively reduce the loss of bone mass; however, they can lead to atypical femoral fractures and osteonecrosis of the jaw with long-term use. Hormone replacement therapy is only recommended for women who also have menopausal symptoms, and some drugs, such as Raloxifene, can increase the risk of blood clots and strokes. A human monoclonal antibody, Denosumab, is a new drug for the treatment of osteoporosis that has also many side effects, including infections, skin and jawbone problems . Therefore, it is important to seek novel therapies and treatments. Many herbs have been used to treat osteoporosis and other bone diseases in China and other East Asian countries for many hundreds of years, but the mechanisms have not been completely elucidated. Icaritin (ICT) is a hydrolytic product of icariin from the genus Epimedium, a traditional Chinese herbal medicine used as a bone protective agent for over one thousand years. ICT has many indicated pharmacological and biological activities, including growth inhibition or apoptosis induction of a variety of cancer cells , , , , ,  and human prostatic smooth muscle cells ; enhancement of the radiosensitivity of 4T1 breast cancer cells ; attenuation of LPS-induced inflammation ; cardioprotective and neuroprotective effects , , , . Regarding bone metabolism, ICT can also enhance the differentiation and activity of osteoblasts while suppressing osteoclastic differentiation in vitro , stimulate osteogenic differentiation and inhibit adipogenesis of mesenchymal stem cells , , and reduce the incidence of steroid-associated osteonecrosis with inhibition of both thrombosis and lipid-deposition . However, the signaling pathways of these processes have not been elucidated.