Quantitative photometrical assessment of iron deposits in synovial membranes in different joint diseases

Theaflavin-3,3'-Digallate Inhibits Erastin-Induced Chondrocytes Ferroptosis via the Nrf2/GPX4 Signaling Pathway in Osteoarthritis

There is evidence that osteoarthritis (OA) is associated with ferroptosis which is a kind of lipid peroxidation-related cell death. Theaflavin-3,3'-digallate(TF3), a polyphenol compound extracted from black tea, possesses antioxidative and anti-inflammatory properties, but its effects on chondrocyte ferroptosis in osteoarthritis (OA) remain unclear. Our present study aims at exploring the protective role and underlying mechanisms of TF3 against erastin-induced chondrocyte ferroptosis in OA. In human primary chondrocytes treated with erastin alone or combined with different doses of TF3, cell viability was assessed by MTS. Ferroptosis-related proteins, including Gpx4, HO-1, and FTH1, were detected by western blot. The levels of lipid peroxidation and Fe2⁺ were determined by fluorescence staining. Meanwhile, the change of related proteins in the Nrf2/Gpx4 signaling pathway was determined by western blot. siRNA-mediated Nrf2 knockdown and the Gpx4 inhibitor RSL3 were used to explore molecular mechanisms for TF3-induced ferroptosis in OA chondrocyte. The magnetic resonance imaging (MRI), HE staining, Masson's staining, and immunohistochemistry were used to evaluate articular cartilage damages in the rat OA model. The results showed that Gpx4 expression was markedly downregulated in the chondrocytes of OA patients. TF3 reversed erastin-induced ferroptosis of human cultured chondrocytes, lipid ROS, and Fe2⁺ production in mitochondria. Moreover, the expression of Gpx4, HO-1, FTH1, and Nrf2 was markedly induced by TF3 in the erastin-treated chondrocytes. The antiferroptotic effect of TF3 was related to enhance Nrf2/Gpx4 signaling pathway. Finally, TF3 inhibited OA progression by alleviating in vivo cartilage damage related to chondrocyte ferroptosis. Thus, TF3 significantly inhibits chondrocyte ferroptosis by activating the Nrf2/Gpx4 signaling pathway, suggesting that TF3 serves as a potential therapeutic supplement for OA treatment.

The Comparison of Inflammatory Markers for the Prediction of Recurrence of the Nasal Polyp After Endoscopic Sinus Surgery

During the past decade, several inflammation-based periferic prognostic systems have been reported in the field of chronic rhinosinusitis with nasal polyps (CRSwNP). Recently, C-reactive protein (CRP) and albümin ratio (CAR) showed its impact on a large variety of diseases conditions that cause chronic inflammation. We aimed to compare the inflammatory markers in patients with recurrent and non-recurrent nasal polyps and if a significant inflammatory profile is associated with multiple recurrences. The study concerned 144 patients who underwent FESS for CRSwNP from 2012 to 2017 and had a postoperative follow-up longer than 12 months and 120 healthy individuals. We evaluated the impact of the CAR, neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio, eosinophil-to-lymphocyte ratio (ELR) between patients with and without polyp recurrences and control groups. There was a statistically significant difference in CRP, CAR and ELR values between multiple recurrence group and no-recurrence group (p = 0.02; 0.004; 0.019 respectively), mean eosinophil and CRP values, CAR, NLR and ELR was significantly higher in NP patients than control group (p < 0.001). The receiver operating curve analysis showed CAR and ELR as a potential marker of recurrence of NP (AUC = 0.713 and 0.613, respectively p < 0.001). The cutoff values for were 1.03 for CAR and 0.22 for ELR. The mean CRP, CAR and ELR were significantly higher in patients with CRSwNP whose disease recurred after surgery. CAR may be a potential marker to predict the recurrence before endoscopic sinus surgery as well as ELR in CRSwNP disease.

Ferroptosis in Rheumatoid Arthritis: A Potential Therapeutic Strategy

Ferroptosis is one of the newly discovered forms of cell-regulated death characterized by iron-dependent lipid peroxidation. Extensive research has focused on the roles of ferroptosis in tumors, blood diseases, and neurological diseases. Some recent findings have indicated that ferroptosis may also be related to the occurrence and development of inflammatory arthritis. Ferroptosis may be a potential therapeutic target, and few studies in vitro and animal models have shown implications in the pathogenesis of inflammatory arthritis. This mini review discussed the common features between ferroptosis and the pathogenesis of rheumatoid arthritis (RA), and evaluated therapeutic applications of ferroptosis regulators in preclinical and clinical research. Some critical issues worth paying attention to were also raised to guide future research efforts.

Icariin enhances cell survival in lipopolysaccharide-induced synoviocytes by suppressing ferroptosis via the Xc-/GPX4 axis

The mechanism of action of synovitis, as the vital pathological process of rheumatoid arthritis and osteoarthritis, remains to be elucidated. The effects and the mechanism of icariin (ICA), which is a promising therapeutic agent in synovitis, was investigated in the present study. In addition, ferroptosis, a vital cell process involved in several diseases, was also studied in synovitis for the first time. Lipopolysaccharide (LPS)-induced synoviocytes served as a synovitis cell model. The cells were divided into control, LPS and experimental groups and were treated with different concentrations of ICA. Cell viability was determined by Cell Counting Kit-8 assay and cell death was determined by flow cytometry. The expression levels of proteins (GPX4, SLC7A11, SLC3A2L, TRF, Nrf2 and NCOA4) were measured by western blotting. Quantification of malondialdehyde (MDA), iron and glutathione peroxidase 4 (GPX4) activity levels were performed via using corresponding assay kits. Cell death was increased, and cell viability was decreased in LPS-induced synoviocytes. Furthermore, MDA levels and iron content were elevated and GPX levels was reduced in LPS-induced synoviocytes. Transferrin receptor protein 1 and nuclear receptor coactivator 4 were upregulated and proteins of the Xc-/GPX4 axis, as well as nuclear factor erythroid 2-related factor 2, were decreased by LPS treatment. All aforementioned LPS affects were alleviated by ICA via a concentration-dependent manner. ICA counteracted the effects of RSL3, a ferroptosis activator, on cell viability, lipid peroxidation, iron content and relative protein expression of ferroptosis in synoviocytes. ICA protects the cells from death in synoviocytes induced by LPS, via the inhibition of ferroptosis by activating the Xc-/GPX4 axis, which can be exploited as a new therapeutic strategy for synovitis.

Iron accumulation in senescent cells is coupled with impaired ferritinophagy and inhibition of ferroptosis

Cellular senescence is characterised by the irreversible arrest of proliferation, a pro-inflammatory secretory phenotype and evasion of programmed cell death mechanisms. We report that senescence alters cellular iron acquisition and storage and also impedes iron-mediated cell death pathways. Senescent cells, regardless of stimuli (irradiation, replicative or oncogenic), accumulate vast amounts of intracellular iron (up to 30-fold) with concomitant changes in the levels of iron homeostasis proteins. For instance, ferritin (iron storage) levels provided a robust biomarker of cellular senescence, for associated iron accumulation and for resistance to iron-induced toxicity. Cellular senescence preceded iron accumulation and was not perturbed by sustained iron chelation (deferiprone). Iron accumulation in senescent cells was driven by impaired ferritinophagy, a lysosomal process that promotes ferritin degradation and ferroptosis. Lysosomal dysfunction in senescent cells was confirmed through several markers, including the build-up of microtubule-associated protein light chain 3 (LC3-II) in autophagosomes. Impaired ferritin degradation explains the iron accumulation phenotype of senescent cells, whereby iron is effectively trapped in ferritin creating a perceived cellular deficiency. Accordingly, senescent cells were highly resistant to ferroptosis. Promoting ferritin degradation by using the autophagy activator rapamycin averted the iron accumulation phenotype of senescent cells, preventing the increase of TfR1, ferritin and intracellular iron, but failed to re-sensitize these cells to ferroptosis. Finally, the enrichment of senescent cells in mouse ageing hepatic tissue was found to accompany iron accumulation, an elevation in ferritin and mirrored our observations using cultured senescent cells.

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Altered iron homeostasis in senescent cells is driven by impaired ferritinophagy.

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Impaired ferritinophagy causes functional cellular iron deficiency.

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senescent cells are resistant to iron mediated cell death including ferroptosis.

Association of NRAMP1 promoter gene polymorphism with the susceptibility and radiological severity of rheumatoid arthritis

The natural resistant-associated macrophage protein 1 (NRAMP1) has been proposed as a candidate gene for the susceptibility to autoimmune diseases. In this study, the possible role of the functional polymorphism located at the promoter region of NRAMP1 gene in the susceptibility and clinical outcome of rheumatoid arthritis (RA) was investigated. A total of 141 Spanish RA patients and 194 controls previously typed for HLA-DRB1* were genotyped for the NRAMP1 polymorphism. No significant differences in the distribution of frequencies among RA patients and controls were observed. Nevertheless, when patients and controls were stratified according to their HLA shared epitope (SE) status, an increase of 2/2 genotype among SE-negative (SE-) patients with respect to SE- controls was observed (23% vs 7%, OR = 3.74, 95% CI 1.31-10.72). In addition, the possible role of this polymorphism in the clinical course of RA was investigated in a subgroup of 82 patients who were prospectively followed during a mean of 9 years. After follow-up, an increase of patients with the homozygous 2/2 genotype was detected among those with severe small joint radiological involvement: 73% of patients 2/2 had a severe form in contrast to 37% of patients with the genotype 2/3 and 30% of patients bearing 3/3 OR = 5.45, 95% CI 1.14-34.24). In conclusion, NRAMP1 gene promoter polymorphism could influence the radiological severity of rheumatoid arthritis and disease susceptibility, particularly in individuals lacking HLA-linked risk factors.

Solute carrier 11a1 (Slc11a1; formerly Nramp1) regulates metabolism and release of iron acquired by phagocytic, but not transferrin-receptor-mediated, iron uptake

Solute carrier 11a1 (Slc11a1; formerly Nramp1; where Nramp stands for natural-resistance-associated macrophage protein) is a proton/bivalent cation antiporter that localizes to late endosomes/lysosomes and controls resistance to pathogens. In the present study the role of Slc11a1 in iron turnover is examined in macrophages transfected with Slc11a1(Gly169) (wild-type) or Slc11a1(Asp169) (mutant=functional null) alleles. Following direct acquisition of transferrin (Tf)-bound iron via the Tf receptor, iron uptake and release was equivalent in wild-type and mutant macrophages and was not influenced by interferon-gamma/lipopolysaccharide activation. Following phagocytosis of [(59)Fe]Tf-anti-Tf immune complexes, iron uptake was equivalent and up-regulated similarly with activation, but intracellular distribution was markedly different. In wild-type macrophages most iron was in the soluble (60%) rather than insoluble (12%) fraction, with 28% ferritin (Ft)-bound. With activation, the soluble component increased to 82% at the expense of Ft-bound iron (<5%). In mutant macrophages, 40-50% of iron was in insoluble form, 50-60% was soluble and <5% was Ft-bound. Western-blot analysis confirmed failure of mutant macrophages to degrade complexes 24 h after phagocytic uptake. Confocal microscopy showed that complexes were within lysosome-associated membrane protein 1-positive vesicles in wild-type and mutant macrophages at 30 min and 24 h, implying failure in the degradative process in mature phagosomes in mutant macrophages. NO-mediated iron release was 2.4-fold higher in activated wild-type macrophages compared with mutant macrophages. Overall, our data suggest that iron acquired by phagocytosis and degradation is retained within the phagosomal compartment in wild-type macrophages, and that NO triggers iron release by direct secretion of phagosomal contents rather than via the cytoplasm.

Natural-resistance-associated macrophage protein 1 is an H+/bivalent cation antiporter

In mammals, natural-resistance-associated macrophage protein 1 (Nramp1) regulates macrophage activation and is associated with infectious and autoimmune diseases. Nramp2 is associated with anaemia. Both belong to a highly conserved eukaryote/prokaryote protein family. We used Xenopus oocytes to demonstrate that, like Nramp2, Nramp1 is a bivalent cation (Fe2+, Zn2+ and Mn2+) transporter. Strikingly, however, where Nramp2 is a symporter of H+ and metal ions, Nramp1 is a highly pH-dependent antiporter that fluxes metal ions in either direction against a proton gradient. At pH 9.0, oocytes injected with cRNA from wild-type murine Nramp1 with a glycine residue at position 169 (Nramp1(G169); P=3.22x10(-6)) and human NRAMP1 (P=3.87x10(-5)) showed significantly enhanced uptake of radiolabelled Zn2+ compared with water-injected controls. At pH 5.5, Nramp1(G169) (P=1.34x10(-13)) and NRAMP1 (P=1.09x10(-6)) oocytes showed significant efflux of Zn2+. Zn2+ transport was abolished when the proton gradient was dissipated using carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Using pre-acidified oocytes, currents of 130+/-57 nA were evoked by 100 microM Zn2+ at pH 7.5, and 139+/-47 nA by 100 microM Fe2+ at pH 7.0, in Nramp1(G169) oocytes; currents of 254+/-49 nA and 242+/-26 nA were evoked, respectively, in NRAMP1 oocytes. Steady-state currents evoked by increasing concentrations of Zn2+ were saturable, with apparent affinity constants of approx. 614 nM for Nramp1(G169) and approx. 562 nM for NRAMP1 oocytes, and a curvilinear voltage dependence of transporter activity (i.e. the data points approximate to a curve that approaches a linear asymptote). In the present study we propose a new model for metal ion homoeostasis in macrophages. Under normal physiological conditions, Nramp2, localized to early endosomal membranes, delivers extracellularly acquired bivalent cations into the cytosol. Nramp1, localized to late endosomal/lysosomal membranes, delivers bivalent cations from the cytosol into this acidic compartment where they may directly affect antimicrobial activity.

Local and systemic responses to iron-dextran injected into a granuloma pouch in the rat

Many inflammatory processes are accompanied by anemia and repeated hemorrhages, but the local and systemic effect of the iron present in the inflamed area and the availability of this iron are not known. The experimental model used to mimic the above situation was the carrageenan-induced granuloma in rats with simultaneous iron-dextran injection into the granuloma pouch. We studied the effect of iron-dextran on leukocytes from the inflammatory exudate and the location of iron in the granuloma tissue. We also evaluated the systemic responses by studying several iron parameters in blood and in iron-storage organs. The results showed a reduction in the number of leukocytes present in the exudate and a reduction in their viability and also extensive damage to the granuloma tissue, essentially to macrophages, caused by local iron-induced oxidative stress. A small percentage of iron reaches the systemic circulation, and this is eventually stored in the liver and spleen as hemosiderin, which is unlikely to have any effect on anemia. In spite of its local toxicity, the accumulation of iron in inflamed areas can be interpreted as a protective mechanism against systemic oxidative radical reactions induced by iron mobilization.

Genetic regulation of macrophage activation: understanding the function of Nramp1 (=Ity/Lsh/Bcg)

The Nramp1 gene was originally described as Ity/Lsh/Bcg, a single gene controlling resistance and susceptibility of inbred mice to a range of intramacrophage pathogens. Functional studies demonstrated that Ity/Lsh/Bcg had multiple pleiotropic effects on macrophage activation pathways, broadening interest in the gene to include its candidacy as an autoimmune disease susceptibility gene. In 1993 the gene was positionally cloned and found to encode a polytopic integral membrane protein of unknown function. Subsequent studies have localized the protein to late endosomal and lysosomal compartments, and demonstrated that it functions as an iron transporter. Precisely how this function influences macrophage activation pathways is still under investigation, but is likely to include direct effects on pathogen survival in the endosomal/lysosomal compartment as well as influences on intracellular signalling pathways and in regulating mRNA stability. Several studies now provide evidence for a role for NRAMP1 in determining human susceptibility to autoimmune (rheumatoid arthritis. juvenile rheumatoid arthritis, diabetes, Crohn's disease) and infectious (tuberculosis, leprosy) diseases. Amongst these. data are accumulating to support the hypothesis that a functional Z-DNA forming repeat polymorphism in the promoter region of human NRAMP1 contributes directly to disease susceptibility. Four alleles have been observed, alleles 1 and 4 are rare (gene frequencies approximately equal to 0.001), alleles 2 and 3 occur at gene frequencies approximately 0.25 and approximately 0.75, respectively. In the absence of exogenous stimuli, alleles 1, 2 and 4 are poor promoters of gene expression in a luciferase reporter gene system; allele 3 drives high expression. Allele 3 shows allelic association with autoimmune disease susceptibility, allele 2 with infectious disease susceptibility. Hence, balancing selection is likely to be maintaining these two alleles in human populations. Although the association of NRAMP1 with autoimmune disease susceptibility may be related to any one of the multiple pleiotropic effects associated with macrophage activation, the function of NRAMP1 as an iron transporter now prompts more interesting speculation that regulation of iron transport may contribute directly to the disease phenotype in arthritic disease. Patients suffering from rheumatoid arthritis show increased deposition of iron in the synovial membrane, which may contribute to free radical generation and local inflammation. Further analysis of NRAMP1 function will continue to be of importance in understanding the molecular basis to autoimmune and infectious disease susceptibility.