## 4 Discussion
In senescent cells, ROS production is abnormally enhanced [39; 40] and SA-\(\beta\)-gal specifically exists in senescent cells [41]. In addition, senescent cells secrete various factors, such as inflammatory cytokines and MMPs [42; 43]. Therefore, cellular senescence is closely associated with not only ROS, but also inflammatory cytokines and MMPs. The present study showed that CDDP increased ROS production in oral mucosa-derived cells and the rate of SA-\(\beta\)-gal-positive cells. However, no significant differences were observed in ROS production or the rate of SA-\(\beta\)-gal-positive cells between CDDP- and CDDP+\(\beta\)-cry-treated cells, which was in contrast to the results obtained on inflammatory cytokines and MMPs. In other words, CDDP promotes biological oxidation and senescence, which may not be inhibited by \(\beta\)-cry. The reasons for this are unknown, but may be related to the smaller changes in ROS and SA-\(\beta\)-gal caused by CDDP rather than those in inflammatory cytokines and MMPs. Previous studies reported that astaxanthin and coenzyme Q10 have similar antioxidant functions to \(\beta\)-cry [44; 45]. Keratinocyte growth factor (KGF) may reduce the risk of oral mucositis in adults receiving radiotherapy with CDDP for head and neck cancers or chemotherapy for a mixture of solid and blood cancers [46; 47]. Dermal toxicity (exanthema, erythema, edema, and pruritus), oral toxicity (abnormal sensation, discoloration of the tongue, pachyglossia, and changes in the taste), and pain may occur as adverse reactions. KGF receptors are present even in malignant epithelial cells, as demonstrated for other growth factors; therefore, KGF may stimulate the division/growth of malignant cells expressing KGF receptors. On the other hand, the naturally derived ingredient \(\beta\)-cry has been shown to decrease the number of gastric cancer cells and MMP-2/MMP-9 production and also reduce the volume and weight of tumors, inhibiting tumor growth through the induction of apoptosis [48]. Furthermore, \(\beta\)-cry levels were found to be lower in patients with severe periodontal disease in all age groups of all races. An observational study reported a strong correlation between fruit/vegetable/other antioxidant nutrient intakes and quality of life associated with adult oral health [49]. In our previous study on 5-FU, only oral mucosa-derived epithelial cells were used. However, chemotherapy-related oral mucositis is also caused by damage to oral mucosal fibroblasts in not only oral mucosal epithelial cells, but also the inherent mucosal layer. Therefore, the present study investigated fibroblasts in addition to epithelial cells. In the future, this issue needs to be investigated in more detail in vivo. The present results suggest that CDDP damages epithelial cells and fibroblasts comprising the oral mucosa and causes oral mucositis by inducing cellular senescence and increasing ROS production and inflammatory cytokine/MMP expression/production. Furthermore, \(\beta\)-crgy may attenuate CDDP-related oral mucositis and maintain the QOL of patients. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15094803/s1](https://www.mdpi.com/article/10.3390/app15094803/s1)]([https://www.mdpi.com/article/10.3390/app15094803/s1](https://www.mdpi.com/article/10.3390/app15094803/s1)), Figure S1: Assessment of viability of CDDP-treated hOMK and hOMF in the range of 0.01-100 \(\mu\)g/mL; Figure S2: Changes in the morphology of hOMK and hOMF after the treatment with CDDP. Table S1: Primer probes used for quantitative RT-PCR. Conceptualization, T.Y. and K.Y. ; Methodology, N.W. ; Formal analysis, N.W. ; Investigation, K.Y., N.W. and F.O. ; Resources, O.M. and N.K. ; Data curation, F.O. ; Writing--original draft, T.Y. ; Writing--review & editing, K.Y. and O.M. ; Supervision, K.Y., F.O., O.M. and N.K. ; Project administration, T.Y. and N.K. ; Funding acquisition, T.Y., K.Y. and F.O. All authors have read and agreed to the published version of the manuscript.