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We previously reported that treatment of icariin could significantly induce cardiomyocyte differentiation of murine embryonic stem (ES) cells in vitro. In the present study, the exact activity initiated by icariin was further confirmed and the underlying molecular mechanism was investigated. We found that cardiomyocyte differentiation was efficiently stimulated only if icariin was administrated between days 5 and 8 in differentiation course, which indicated with elevated percentage of embryoid bodies (EB) and with beating areas and up- regulated expression of alpha-actinin and troponin T. Exposure of icariin triggered intracellular reactive oxygen species (ROS) generation of EBs in 3 h, which was abolished in the presence of either NADPH oxidase inhibitor DPI or antioxidant Trolox. Meanwhile, expression of NOX4, a membrane combined enzyme responsible for ROS generation, was promoted by icariin in a dose-dependent manner. Although p38MAPK (mitogen-activated protein kinase), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal protein kinase (JNK) were spontaneously activated in early differentiation, only the phosphorylation of p38MAPK was enhanced and prolonged when icariin was present, whereas both ERK and JNK showed no response to icariin treatment. Moreover, the inducible effect of icariin was blunted by SB203580, a specific inhibitor of p38MAPK. On the contrary, neither UO126 nor SP600125, the specific inhibitor of ERK and JNK, could abolish icariin-stimulated differentiation. Nuclear location of MEF2C, which played a critical role in cardiomyocyte differentiation and could be activated by p38MAPK, was stimulated after icariin exposure. Taken together, these results suggest that ROS generation and the subsequent activation of p38MAPK are essential for the inducible function of icariin on cardiomyocyte differentiation of murine embryonic stem cells in vitro.

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The significant promoting effects of some prenylflavonoids on cardiac differentiation of mouse embryonic stem (ES) cells via reactive oxygen species (ROS) signaling pathway were investigated. The most effective differentiation was facilitated by icariin (ICA), followed by icaritin (ICT), while desmethylicaritin (DICT) displayed the weakest but still significant inducible effect. Contrarily, DICT demonstrated the strongest anti-oxidative activity while ICA displayed only little in vitro, which was well matched with the hydroxyl (OH) numbers and the positions in the molecular structures. Therefore, ROS signaling cascades were assumed to be involved in prenylflavonoids induced cardiomyogenesis. Treatment with ICA, intracellular ROS in embryoid bodies was rapidly elevated, which was abolished by the NADPH-oxidase inhibitor apocynin; elimination of intracellular ROS by vitamin E or pyrrolidine dithiocarbamate (PDTC) inhibited ICA induced cardiomyogenesis; ROS-sensitive extracellular-regulated kinase 1, 2 (ERK1, 2) and p38 activation were further observed, the cardiomyogenesis was significantly inhibited in the presence of ERK1, 2 or p38 inhibitor U0126 or SB203580, indicating the roles of NADPH-ROS-MAPKs signaling cascades in prenylflavonoids induced cardiac differentiation. There was no difference in Nox4 NADPH oxidase expression between ICA and ICT treatments, however, ROS concentration in EBs after ICT administration was lower than that after ICA treatment, followed by less activation of ERK1, 2, and p38. These results revealed that the significant promoting effects of prenylflavonoids on cardiac differentiation was at least partly via ROS signaling cascades, and the facilitating abilities preferentially based on the nature of prenylflavonoids themselves, but anti-oxidative activity determined by the OH numbers and the positions in the structures do influence the cardiomyogenesis in vitro.

A concise algorithm is proposed in this paper for the calculation of the factor of safety of a slope using the Morgenstern–Price method. Based on force and moment equilibrium considerations, two expressions are derived for the factor of safety Fs and the scaling factor λ, respectively, both in relatively simple forms. With this algorithm and assumed initial values of Fs and λ, the solutions for Fs and λ are found to converge within a few iterations. Compared to other procedures, the present algorithm possesses the advantages of simplicity and high efficiency in application. It is rather straightforward to implement this algorithm into a computer program.Key words: slope, stability, factor of safety, limit equilibrium method.