Excessive chemical and dynamic stimulation to a cell increases oxidative stress in the cell and causes cellular dysfunction. Osteoblast counts decrease under oxidative stress, and it is known that in the healing process after surgical treatment, bone regeneration treatment, bone fracture, and dental implant treatment, apoptosis is induced, and there is a decrease in bone tissue. In addition, hydrogen peroxide induces cell death via oxidative stress, and vitamin B is known to be involved as a coenzyme of the oxidation-reduction reaction. However, the effects of vitamin B on tissues and cells remain unclear. In this study, we investigated the effects of a vitamin B3, nicotinamide (NAm), on the cytotoxicity induced by hydrogen peroxide. In this study, osteoblasts-like cells derived from Sprague-Dawley rat marrow were cultured. NAm was added to the culture medium for pretreatment, and hydrogen peroxide was added for cytotoxic treatment. A phase contrast microscope was used to observe the morphology of the treated cells, and water-soluble tetrazolium salt-8-based colorimetry was used for evaluating the number of attached cells. Changes in cell shape and decreased cell attachment were observed after cytotoxic treatment with hydrogen peroxide. These changes were not observed in cells treated with only the NAm pretreatment. However, in cells treated with both the NAm pretreatment and the cytotoxic treatment, NAm pretreatment inhibited the changes in cell shape and the decrease in cell attachment. In conclusions, pretreatment with NAm inhibited the cytotoxic treatment-induced morphological changes and decrease in cell attachment. The results suggest that NAm might inhibit cytotoxicity, including apoptosis. As such, NAm may be a promising candidate adjuvant for bone regeneration treatments. However, in the NAm-pretreated cells, the cytotoxic effects of hydrogen peroxide on cell morphology were observed later, and they appeared to progress with time. From this, it appears that NAm affects the time progress of the cytotoxicity resulting from oxidative stress.
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