Effects of natural iron chelators on dendritic cells: anti-inflammatory activity, phenotypic characterization, and metabolomic analysis

Dendritic cells (DCs) are key regulators of the immune system that patrol all the compartments of the body. When exposed to danger signals, DCs mature, migrate to the draining lymph nodes, and activate the adaptive immune response. Significant differences exist between immature DCs (iDCs) and mature DCs (mDCs), the first guard the host periphery and support homeostasis, and the second present antigens and support inflammation. Bacteria are among the most common maturational stimuli that cause the switch from iDCs to mDCs. DCs can also be divided by lineage into myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs). They are both present in mucosal tissues and regulate the immune response by secreting chemokines and cytokines. Several key elements play an important role in this process, among those, intracellular iron is an underinvestigated player required to initiate and sustain their inflammatory response. It has been recently demonstrated that the exposure of DCs to naturally derived iron chelators reduce the intracellular iron pool and, consequently, prevents DCs’ secretion of inflammatory cytokines and antigen­presenting abilities. Iron content in the body is finely regulated, but several pathologies, as well as diet, may affect its level. Little is known about the effects of DCs maturation in iron overload conditions or iron­deprived conditions. The aim of the PhD work will be the investigation of the metabolic pathways characterizing DCs in resting and active conditions and identify the potential protective effects of nutritional­derived biochelators in a murine model of chronic intestinal inflammation. This research work can be divided into three phases: the first consisted of the study of the role of iron in the maturational process of DCs, the second analyzed the metabolomic profile of active and inactivated DCs while the third involved the use of a mouse model of chronic colitis to study the effects of polyphenols in vivo. The results clearly describe the role of iron in the maturational process of DCs as cells cultured in an iron­enriched culture medium for ten days failed to differentiate into conventional CD11c+MHCIIhi DCs and respond to LPS. Phenotypically, these cells appeared smaller than control DCs but vital and able to perform FITC­dextran endocytosis. DCs activation is linked to metabolic changes that are essential to support their activity and function. Hence, targeting DCs metabolism represents an opportunity to modify the inflammatory and immune response. Using untargeted metabolomics, it was possible to evaluate the modulation of mDCs metabolism after stimulation with LPS and assess polyphenol effects. Both fraction C derived from Humulus lupulus and quercetin reduced the production of several inflammatory cytokines, but differently from quercetin, the fraction C mechanism was independent of extracellular iron and showed a different metabolic pathway. The last part of the work studied the effects of anthocyanins derived from B1 Pl1 purple corn cobs through ethanol extraction on a mouse model of chronic colitis: the SAMP1/YitFc. These mice develop spontaneous ileitis that resembles human Crohn’s disease with a typical discontinuous pattern. After 70 days of anthocyanin intervention, we observed positive changes in the histology score and microbial populations. .. [edited by Author]