Figure 6
From: Reduced post-operative DPP4 activity associated with worse patient outcome after cardiac surgery
DPP4 oxidation is induced during cardiac surgery and decreases DPP4 activity. (a) Quantification of oxidized amino acids of DPP4 peptides from serum of patients before (Pre-OP) vs. after (Post-OP) cardiac surgery (oxidized amino acids: lysine, histidine, methionine, tryptophane) using MALDI mass-spectrometry (n = 10). Shown are means ± SD. Two-tailed t-test. **P < 0.01. (b) Characteristic MALDI-TOF mass-spectrum of trypsinized DDP4 protein isolated from serum of a patient after cardiac surgery. The arrow at 809.2 Da indicates the mass signal of the oxidized DDP4fragment NTYRLK*, with K* the oxidized amino acid lysine. (c) Characteristic mass fingerprint spectra of trypsinized recombinant human DPP4, before (left) and after (right) in vitro oxidation with H2O2 (representative for 3 experiments). The arrow in the right panel indicates the mass signal of the oxidized DDP4 fragment NTYRLK* at 809.2 Da, which was not detected (n.d.) before oxidation (left panel). Mass signals were normalized to the internal standard (C13 Ang II). (d) Quantification of the activity of in vitro oxidized DPP4 (ox. DPP4) versus native recombinant human DPP4. To evaluate potential effects of residual H2O2 after extensive dialysis on DPP4 activity, a “H2O2 control sample” lacking DPP4 was dialyzed in the same way, after which DPP4 was added to the same final concentration as the oxidized DPP4 after dialysis (“control”). n = 3. Shown are means ± SD. One-way ANOVA (Kruskal Wallis) with Dunn’s post-test. *P < 0.05; n.s. = not significant.
