Figure 4

Effect of carnosine on gene expression. TNF-α stimulated HUVECS were exposed to 0 µM, 400 µM or 800 µM methylglyoxal (MGO) in the presence or absence of carnosine (CN, 20 mM) for 24 hours. Gene expression profiling was performed by microarray analysis. Displayed are the p-value distribution across all examined genes (A,C) and the corresponding volcano plot (B and D) for the comparisons 0 µM MGO no CN vs. 0 µM MGO + 20 mM CN (upper panel) and 800 µM MGO no CN vs. 800 µM MGO + 20 mM CN (lower panel). (A) The p-value distribution across all genes shows a homogenous pattern indicating that CN did not significantly affect the gene expression profile of TNF-α stimulated HUVECs. (B) The corresponding volcano plot analysis revealed only three genes to be significantly affected by CN as compared to control. (C) The p-value distribution shows a relative excess of p-values < 0.05, though this effect was less pronounced as compared to the p-value distribution in Fig. 3A. (D) The corresponding volcano plot analysis revealed 37 genes to be significantly affected by CN. Multiple hypothesis testing was accounted for by application of false discovery correction. The significance threshold for adjusted p-values in all analyses was defined as 0.05, which corresponds to the nominal significance thresholds represented by the horizontal lines in B and D. The different nominal threshold values result from the experiment-dependent multiplicity adjustment. Vertical lines represent thresholds for FC ≥ ±1.5 (Log₂ (FC) ≤ −0.5 or Log₂ (FC) ≥ 0.5).