**5. Conclusions**

Despite these limitations, our data provide evidence that circulating AOPP and TBARS levels are significantly elevated in CD patients with severe relapse, suggesting that these parameters could be evaluated in a prospective, larger study on the progression of CD disease, as biomarkers for diagnosis or monitoring of CD patients. Moreover, our results indicate that AOPP/AGEs activation of RAGE signaling should be explored for diagnostic or therapeutic purposes in immune-mediated diseases such as CD.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3921/8/9/378/s1. Table S1: Correlations among markers of oxidative stress in Crohn's patients, Table S2: Correlations among markers of oxidative stress in healthy volunteers.

**Author Contributions:** Conceptualization, M.L. and C.M.; data curation, C.M.; formal analysis, C.L.; investigation, S.A.; methodology, M.L. and E.B.; original draft preparation, C.L.; writing—review and editing, C.L. and E.B.; patient qualification for the study and clinical material collection F.G., F.F., S.S. and D.Z.; project administration, M.L. and C.M.; funding acquisition, M.L., C.M. and F.G.

**Funding:** This research was supported by grants from Ente Cassa di Risparmio di Firenze (2016.0842 and 2017. 0841) and by the University of Florence (Fondi di Ateneo).

**Acknowledgments:** We thank all the patients and the healthy volunteers who participated in this study.

**Conflicts of Interest:** The authors declare that they have no conflicts of interest.
