Objective: To analyse the role played by Sappanone A, a bioactive ingredient isolated from the heartwood of Caesalpinia sappan, in the regulation of oral epithelial cell viability under radiation. Methods: Cell viability of human oral keratinocytes (HOKs) and mouse salivary gland cells under ionising radiation was analysed. Expression of Ki67 was measured by immunohistochemical staining. Fragmentation of deoxyribonucleic acid (DNA) was measured by comet assay. Cell death was analysed using trypan blue exclusion assay. Cell viability was measured using a Cell Counting Kit 8 (CCK8; Abcam, Cambridge, UK) assay.
Results: Sappanone A decreased cell viability of HOK cells and mouse salivary gland cells under ionising radiation. In addition, Sappanone A enhanced radiation-induced genomic DNA fragmentation, accompanied by impaired homologous recombination and non-homologous end joining DNA repair. Mechanistic evaluation revealed that Sappanone A counteracted radiation-induced inosine monophosphate dehydrogenase 2 (IMPDH2) activation, and that this effect could be abolished by reconstituted expression of a Sappanone A-binding defective IMPDH2 mutant.
Conclusion: The present study highlights a novel role played by Sappanone A in the modulation of radiosensitivity of oral epithelial cells.