Figure 4.

Influence of the OGDHC inhibitor SP on p21-dependent responses of NAD(P)H:XTT reductase activity of A549 cells to variation in the thiamine/ThDP levels. A549^wt (A,C,E,G) or A549^p21- (B,D,F,H) cells were cultured in DMEM prepared with 4 mg/L thiamine hydrochloride (Control, A, B, E, F) or without thiamine (Thiamine deficiency, C, D, G, H). 24 h after supplementation with indicated concentrations of ThDP (shades of grey) and/or SP (4.5 mM, hatched columns), NAD(P)H:XTT reductase activity was assayed. Values obtained without ThDP supplementation are presented by white columns, those at 0.05 or 5 mM ThDP—by gray or black columns, correspondingly. In the upper part (A–D), cellular NAD(P)H:XTT reductase activity is normalized to the activity of the control A549^wt or A549^p21- cells to show the combined effects of thiamine/ThDP and SP on cellular viability. In the lower part (E–H), cellular NAD(P)H:XTT reductase activity is normalized to the corresponding value without SP to show the specific effect of SP under each the varied thiamine/ThDP levels. The data of at least three independent experiments are presented as mean ± SEM. Statistically significant differences (p < 0.05, shown by asterisks) are determined by two-way ANOVA followed by Tukey’s post hoc test. Horizontal lines show the groups compared. Asterisks above the bars in C and D indicate the statistically significant differences between the corresponding thiamine deficient cells and cells with the standard thiamine level. Asterisk in G indicates the statistically significant effect of SP vs the same condition without SP. ANOVA significances of the factors (SP and ThDP) and their interactions are given below the graphs, with significant (p < 0.05) values in bold.