Objective(s) Para-Nonylphenol (p-NP) is used in many industries and our previous study showed that p-NP causes a reduction in rats bone marrow mesenchymal stem cells (MSCs) viability. The aim of this study was to investigate the effect of p-NP on osteogenic differentiation of MSCs. Materials and Methods MSCs were isolated and expanded to 3rd passage, then cultured in DMEM supplemented with osteogenic media as well as 0.5 or 2.5 µM of p-NP. After 5, 10, 15, and 21 days, the viability and the level of mineralization was determined using MTT assay and alizarin red, respectively. In addition, morphology and nuclear diameter of the cells were studied with the help of fluorescent dye. Furthermore, calcium content and alkalinphosphatase activity were also estimated using commercial kits. Data were statistically analyzed and the P<0.05 was taken as the level of significance. Results The viability and mineralization of the cells treated with 2.5 µM of p-NP reduced significantly after day 10 in comparison with the control group and administration of 0.5 µM. Moreover, chromatin condensation, reduction of nuclei diameter, and cytoplasm shrinkage was observed in the cell treated with 2.5 µM. The calcium concentration and alkalinphosphatase activity of the cells decreased significantly with 2.5 µM of p-NP when compared with 0.5 µM and control group. Conclusion Adverse effect of p-NP was observed on osteogenic differentiation of MSCs at 2.5 µM due to disruption of mineralization. We strongly suggest more investigations on this chemical with respect to other stem cells, especially skin stem cells as p-NP is used in the formulation of cosmetics
