Formaldehyde-induced SCE levels in cells with defective ADH5 and ALDH2 activities. (A-B) Growth curves (A) and formaldehyde (HCHO) sensitivities (B) of KO HAP1 cell lines with the indicated genotypes. Mean ± standard deviation (SD) in triplicate cultures are shown. (C) SCE levels in HAP1 cells with the indicated genotypes. The points represent the number of SCE events per metaphase, and mean ± standard error of the mean (SEM) are indicated. (D) Quantification of γH2AX foci per cell. The points represent the number of foci per nucleus. Mean ± SEM (n = 500) is shown for each condition. (E) Representative images show spontaneous and formaldehyde (HCHO)-induced formation of γH2AX foci in HAP1 cells. (F) Cell viability was quantified following formaldehyde (HCHO) or MMC treatment (48 hours). Mean ± SD in a quadruplicate experiment are shown. The P values were calculated using 1-way ANOVA with Tukey’s multiple-comparisons test. n.s., not significant.