Type 1 diabetes (T1D), an autoimmune inflammatory disorder, develops as a consequence of pancreatic β-cell destruction and results in hyperglycaemia. Since current T1D therapy mainly involves insulin replacement, the aim of the present study was to evaluate the therapeutic potential ofOriganum vulgareL. ssp.hirtum(Greek oregano) leaf extract rich in biophenols for the treatment of T1D. The phytochemical profile of methanolic oregano extract (MOE) and aqueous oregano extract (AOE) was determined by liquid chromatography/electrospray ion-trap tandem MS (LC/DAD/ESI-MSn), while their main compounds were quantified by HPLC with diode array detection. After establishing their potentin vitroantioxidant activity, the extracts were administered to C57BL/6 mice treated with multiple low doses of streptozotocin for diabetes induction. While prophylactic AOE therapy had no impact on diabetes induction, MOE reduced diabetes incidence and preserved normal insulin secretion. In addition, MOE scavenged reactive oxygen and nitrogen species and, therefore, alleviated the need for the up-regulation of antioxidant enzymes. MOE treatment specifically attenuated the pro-inflammatory response mediated by T helper 17 cells and enhanced anti-inflammatory T helper 2 and T regulatory cells through the impact on specific signalling pathways and transcription factors. Importantly, MOE preserved β-cells fromin vitroapoptosis via blockade of caspase 3. Finally, rosmarinic acid, a predominant compound in MOE, exhibited only partial protection from diabetes induction. In conclusion, acting as an antioxidant, immunomodulator and in an anti-apoptotic manner, MOE protected mice from diabetes development. Seemingly, there is more than one compound responsible for the beneficial effect of MOE.

The main pathological hallmark of diabetes is the loss of functional β‐cells. Among several types of β‐cell death in diabetes, the involvement of ferroptosis remains elusive. Therefore, we investigated the potential of diabetes‐mimicking factors: high glucose (HG), proinflammatory cytokines, hydrogen peroxide (H₂O₂), or diabetogenic agent streptozotocin (STZ) to induce ferroptosis of β‐cells in vitro. Furthermore, we tested the contribution of ferroptosis to injury of pancreatic islets in an STZ‐induced in vivo diabetic model. All in vitro treatments increased loss of Rin‐5F cells along with the accumulation of reactive oxygen species, lipid peroxides and iron, inactivation of NF‐E2‐related factor 2 (Nrf2), and decrease in glutathione peroxidase 4 expression and mitochondrial membrane potential (MMP). Ferrostatin 1 (Fer‐1), ferroptosis inhibitor, diminished the above‐stated effects and rescued cells from death in case of HG, STZ, and H₂O₂ treatments, while failed to increase MMP and to attenuate cell death after the cytokines’ treatment. Moreover, Fer‐1 protected pancreatic islets from STZ‐induced injury in diabetic in vivo model, since it decreased infiltration of macrophages and accumulation of lipid peroxides and increased the population of insulin‐positive cells. Such results revealed differences between diabetogenic stimuli in determining the destiny of β‐cells, emerging HG, H₂O₂, and STZ, but not cytokines, as contributing factors to ferroptosis and shed new light on an antidiabetic strategy based on Nrf2 activation. Thus, targeting ferroptosis in diabetes might be a promising new approach for preservation of the β‐cell population. Our results obtained from in vivo study strongly justify this approach.

Macrophage migration inhibitory factor (MIF) is a multifunctional protein that is involved in the development of gut-related inflammation. To investigate the role of MIF in the function of the intestinal barrier, we have explored intestinal permeability and gut-associated immune response in MIF-deficient (MIF-KO) mice. The absence of MIF provoked impairment of tight and adherens epithelial junctions in the colon through the disturbance of E-cadherin, zonula occludens-1, occludin and claudin-2 expression, which lead to the increase of intestinal barrier permeability. In these circumstances the diversity and content of gut microbiota in MIF-KO mice was considerably different compared to wild type mice. This change in microbiota was accompanied by an increased intestinal IgA concentration and a higher production of pro-inflammatory cytokines TNF and IFN-γ in mesenteric lymph nodes of MIF-KO mice. The forced changes of microbiota executed by antibiotics prevented the “leakage” of the barrier in MIF-KO mice, probably through up-regulation of occludin expression and normalization of cellular pore diameters. In addition, cytokine secretion was normalized after the treatment with antibiotics. These results suggest that MIF participates in the maintenance of physiological microbiota diversity and immunosurveillance, which in turn enables the proper intestinal barrier function.