Iron, lactoferrin and iron regulatory protein activity in the synovium; relative importance of iron loading and the inflammatory response

Heterogeneous ferroptosis susceptibility of macrophages caused by focal iron overload exacerbates rheumatoid arthritis

Focal iron overload is frequently observed in patients with rheumatoid arthritis (RA), yet its functional significance remains elusive. Herein, we report that iron deposition in lesion aggravates arthritis by inducing macrophage ferroptosis. We show that excessive iron in synovial fluid positively correlates with RA disease severity as does lipid hyperoxidation of focal monocyte/macrophages. Further study reveals high susceptibility to iron induced ferroptosis of the anti-inflammatory macrophages M2, while pro-inflammatory M1 are less affected. Distinct glutathione peroxidase 4 (GPX4) degradation depending on p62/SQSTM1 in the two cell types make great contribution mechanically. Of note, ferroptosis inhibitor liproxstatin-1 (LPX-1) can alleviate the progression of K/BxN serum-transfer induced arthritis (STIA) mice accompanied with increasing M2 macrophages proportion. We thus propose that the heterogeneous ferroptosis susceptibility of macrophage subtypes as well as consequent inflammation and immune disorders are potential biomarkers and therapeutic targets in RA.

The role of ferroptosis in intervertebral disc degeneration

Nucleus pulposus, annulus fibrosus, and cartilage endplate constitute an avascular intervertebral disc (IVD), which is crucial for spinal and intervertebral joint mobility. As one of the most widespread health issues worldwide, intervertebral disc degeneration (IVDD) is recognized as a key contributor to back and neck discomfort. A number of degenerative disorders have a strong correlation with ferroptosis, a recently identified novel regulated cell death (RCD) characterized by an iron-dependent mechanism and a buildup of lipid reactive oxygen species (ROS). There is growing interest in the part ferroptosis plays in IVDD pathophysiology. Inhibiting ferroptosis has been shown to control IVDD development. Several studies have demonstrated that in TBHP-induced oxidative stress models, changes in ferroptosis marker protein levels and increased lipid peroxidation lead to the degeneration of intervertebral disc cells, which subsequently aggravates IVDD. Similarly, IVDD is significantly relieved with the use of ferroptosis inhibitors. The purpose of this review was threefold: 1) to discuss the occurrence of ferroptosis in IVDD; 2) to understand the mechanism of ferroptosis and its role in IVDD pathophysiology; and 3) to investigate the feasibility and prospect of ferroptosis in IVDD treatment.

SARS-CoV-2 Infection Dysregulates Host Iron (Fe)-Redox Homeostasis (Fe-R-H): Role of Fe-Redox Regulators, Ferroptosis Inhibitors, Anticoagulants, and Iron-Chelators in COVID-19 Control

Severe imbalance in iron metabolism among SARS-CoV-2 infected patients is prominent in every symptomatic (mild, moderate to severe) clinical phase of COVID-19. Phase-I - Hypoxia correlates with reduced O₂ transport by erythrocytes, overexpression of HIF-1α, altered mitochondrial bioenergetics with host metabolic reprogramming (HMR). Phase-II - Hyperferritinemia results from an increased iron overload, which triggers a fulminant proinflammatory response - the acute cytokine release syndrome (CRS). Elevated cytokine levels (i.e. IL6, TNFα and CRP) strongly correlates with altered ferritin/TF ratios in COVID-19 patients. Phase-III - Thromboembolism is consequential to erythrocyte dysfunction with heme release, increased prothrombin time and elevated D-dimers, cumulatively linked to severe coagulopathies with life-threatening outcomes such as ARDS, and multi-organ failure. Taken together, Fe-R-H dysregulation is implicated in every symptomatic phase of COVID-19. Fe-R-H regulators such as lactoferrin (LF), hemoxygenase-1 (HO-1), erythropoietin (EPO) and hepcidin modulators are innate bio-replenishments that sequester iron, neutralize iron-mediated free radicals, reduce oxidative stress, and improve host defense by optimizing iron metabolism. Due to its pivotal role in 'cytokine storm', ferroptosis is a potential intervention target. Ferroptosis inhibitors such as ferrostatin-1, liproxstatin-1, quercetin, and melatonin could prevent mitochondrial lipid peroxidation, up-regulate antioxidant/GSH levels and abrogate iron overload-induced apoptosis through activation of Nrf2 and HO-1 signaling pathways. Iron chelators such as heparin, deferoxamine, caffeic acid, curcumin, α-lipoic acid, and phytic acid could protect against ferroptosis and restore mitochondrial function, iron-redox potential, and rebalance Fe-R-H status. Therefore, Fe-R-H restoration is a host biomarker-driven potential combat strategy for an effective clinical and post-recovery management of COVID-19.

Can Lactoferrin, a Natural Mammalian Milk Protein, Assist in the Battle against COVID-19?

Notwithstanding mass vaccination against specific SARS-CoV-2 variants, there is still a demand for complementary nutritional intervention strategies to fight COVID-19. The bovine milk protein lactoferrin (LF) has attracted interest of nutraceutical, food and dairy industries for its numerous properties-ranging from anti-viral and anti-microbial to immunological-making it a potential functional ingredient in a wide variety of food applications to maintain health. Importantly, bovine LF was found to exert anti-viral activities against several types of viruses, including certain SARS-CoV-2 variants. LF's potential effect on COVID-19 patients has seen a rapid increase of in vitro and in vivo studies published, resulting in a model on how LF might play a role during different phases of SARS-CoV-2 infection. Aim of this narrative review is two-fold: (1) to highlight the most relevant findings concerning LF's anti-viral, anti-microbial, iron-binding, immunomodulatory, microbiota-modulatory and intestinal barrier properties that support health of the two most affected organs in COVID-19 patients (lungs and gut), and (2) to explore the possible underlying mechanisms governing its mode of action. Thanks to its potential effects on health, bovine LF can be considered a good candidate for nutritional interventions counteracting SARS-CoV-2 infection and related COVID-19 pathogenesis.

RNAseq of Osteoarthritic Synovial Tissues: Systematic Literary Review

Osteoarthritis (OA) is one of the most common causes of disability in aged people, and it is defined as a degenerative arthropathy, characterized by the disruption in joint tissue. The synovium plays a vital role in maintaining the health of the joint by supplying the nutrients to the surrounding tissues and the lubrication for joint movement. While it is well known that all the joint tissues are communicating and working together to provide a functioning joint, most studies on OA have been focused on bone and cartilage but much less about synovium have been reported. The purpose of this review was to investigate the current literature focused on RNA sequencing (RNAseq) of osteoarthritic synovial tissues to further understand the dynamic transcriptome changes occurring in this pivotal joint tissue. A total of 3 electronic databases (PubMed, CINHAL Complete, and Academic Complete) were systematically searched following PRISMA guidelines. The following criteria was used for inclusion: English language, free full text, between the period 2011–2022, size of sample (n > 10), study design being either retrospective or prospective, and RNAseq data of synovial tissue from OA subjects. From the initial search, 174 articles, 5 met all of our criteria and were selected for this review. The RNAseq analysis revealed several differentially expressed genes (DEGs) in synovial tissue. These genes are related to the inflammatory pathway and regulation of the extracellular matrix. The MMP family, particularly MMP13 was identified by three of the studies, indicating its important role in OA. IL6, a key contributor in the inflammation pathway, was also identified in 3 studies. There was a total of 8 DEGs, MMP13, MMP1, MMP2, APOD, IL6, TNFAIP6, FCER1G, and IGF1 that overlapped in 4 out of the 5 studies. One study focused on microbial RNA in the synovial tissue found that the microbes were differentially expressed in OA subjects too. These differentially expressed microbes have also been linked to the inflammatory pathway. Further investigation with more clinical gene profiling in synovial tissue of OA subjects is required to reveal the causation and progression, as well as aid in the development of new treatments.

Iron homeostasis in arthropathies: From pathogenesis to therapeutic potential

Iron is an essential element for proper functioning of cells within mammalian organ systems; in particular, iron homeostasis is critical for joint health. Excess iron can induce oxidative stress damage, associated with the pathogenesis of iron-storage and ageing-related diseases. Therefore, iron levels in body tissues and cells must be tightly regulated. In the past decades, excess iron content within joints has been found in some patients with joint diseases including hemophilic arthropathy, hemochromatosis arthropathy, and osteoarthritis (OA). Currently, increased evidence has shown that iron accumulation is closely associated with multiple pathological changes of these arthropathies. This review summarizes system-level and intracellular regulation of iron homeostasis, and emphasizes the role of iron in synovial alterations, cartilage degeneration, and subchondral bone of several arthropathies. Of note, we discuss the potential link between iron homeostasis and OA pathogenesis. Finally, we discuss the therapeutic potential of maintaining iron homeostasis in these arthropathies.

The Evaluation of 68Ga-Citrate PET/CT Imaging for Dihydroartemisinin in the Treatment of Rheumatoid Arthritis

PURPOSE

We aimed to use 68Ga-citrate, a labeled product of gallium (iron analog), combined with positron emission tomography/computed tomography (PET/CT) to non-invasively evaluate the potential of the iron-responsive product dihydroartemisinin (DHA) in the treatment of rheumatoid arthritis.

PROCEDURES

From the establishment of chicken II collagen-induced arthritis (CIA) rat model over 40 days, 20 rats with one-to-one corresponding arthritis index (AI) scores were randomly divided into two groups. One group received oral DHA (at a dose of 1.5 ml/(kg day), containing 20 mg DHA per 1 ml) for 15 days; the other group received stroke-physiological saline solution (SSS, 1.5 ml/(kg day) for 15 days. 68Ga-citrate micro-PET/CT imaging was performed on day 0 (D0), day 5 (D5), day 10 (D10), and day 15 (D15) of oral administration. After data reconstruction, the cross-sectional length "d" of the ankle joint of each rat was measured on the transverse CT, and the SUVmax of the ankle joint and muscle background was measured for statistical analysis. After micro-PET/CT collection, the ankle joint tissue was observed by HE staining.

RESULTS

The ankle joint swelling in the DHA group was significantly suppressed, but the SSS group showed no significant suppression. 68Ga-citrate micro-PET/CT imaging results and microscope observation confirmed this finding. Statistical analysis indicated that the time tendency of AI score (Binteraction = 0.495, P < 0.001) and T/NT (Binteraction = 1.345, P < 0.001) were discrepant between DHA and SSS groups. The AI score and T/NT of the DHA group gradually increased with time, while the SSS group score gradually decreased. Furthermore, the Spearman correlation coefficient was used to describe the relationship between "d" and T/NT, which was positively correlated (r = 0.855, P < 0.001).

CONCLUSIONS

This study showed that the anti-inflammatory effect of the iron-responsive product DHA in arthritis can be monitored by an iron-like radioactive tracer (68Ga-citrate).

Growth differentiation factor-15 and lactoferrin immuno-expression in breast cancer: relationship with body iron-status and survival outcome

We aimed to evaluate the expression of growth differentiation factor-15 (GDF-15) and lactoferrin (Lf) in tumor and their relationship with the body iron-status and overall survival (OS) outcome of patients with breast cancer. A retrospective cohort study of female patients with primary breast cancer was performed. Clinical tumor samples from the Second Affiliated Hospital of Soochow University between December 2008 and June 2014 were collected. The immuno-expression of GDF-15 and Lf was stratified into positive or negative expression. Kaplan-Meier method and Cox proportional hazards regression model were used for data analysis. 74 breast cancer patients with a mean age of 52 years were included into our study. 14 (18.9%) patients were died by the end of August 1, 2019. The serum iron level of patients with GDF-15 (+)/Lf(-) expression was higher than that of patients with other expression patterns (18.2 ± 5.4 vs. 15.5 ± 5.0 μmol/L, P = 0.038), but was not associated with OS. In univariate Cox analyses, GDF-15(+) and GDF-15(+)/Lf(-) were significantly correlated with high mortality risk (HR = 3.75, 95%CI 1.05-13.48, P = 0.025; HR = 5.00, 95%CI 1.56-16.04, P = 0.004, respectively). After adjusted for age, menopause status and primary tumor grade, the association between GDF-15 and OS disappeared. However, the association between GDF-15/Lf and OS still existed in GDF-15(+)/Lf(-) (HR = 4.50, 95%CI 1.31-15.51, P = 0.017). The combined immuno-expression pattern of GDF-15 and Lf was significant associated with high serum iron level. GDF-15/Lf could be a powerful biomarker to predict survival outcome of patients with breast cancer but still needed to be confirmed by future studies.

Structural aspects of human lactoferrin in the iron-binding process studied by molecular dynamics and small-angle neutron scattering

Lactoferrin is a non-heme protein known for its ability to bind tightly Fe(III) ions in various physiological environments. Due to this feature lactoferrin plays an important role in the processes of iron regulation at the cellular level preventing the body from damages produced by high levels of free iron ions. The X-ray crystal structure of human lactoferrin shows that the iron-binding process leads to conformational changes within the protein structure. The present study was addressed to conformation stability of human lactoferrin in solution. Using molecular dynamics simulations, it was shown that Arg121 is the key amino acid in the stabilization of the Fe(III) ion in the N-lobe of human lactoferrin. The small-angle neutron scattering method allowed us to detect the structural differences between the open and closed conformation of human lactoferrin in solution. Our results indicate that the radius of gyration of apolactoferrin appears to be smaller than that of the hololactoferrin, [Formula: see text] Å and [Formula: see text] Å, respectively. The low-resolution three-dimensional models computed for both forms of human lactoferrin in solution also show visible differences, both having a more compact conformation compared to the high-resolution structure.

Group B Streptococcus Induces Neutrophil Recruitment to Gestational Tissues and Elaboration of Extracellular Traps and Nutritional Immunity

Streptococcus agalactiae, or Group B Streptococcus (GBS), is a gram-positive bacterial pathogen associated with infection during pregnancy and is a major cause of morbidity and mortality in neonates. Infection of the extraplacental membranes surrounding the developing fetus, a condition known as chorioamnionitis, is characterized histopathologically by profound infiltration of polymorphonuclear cells (PMNs, neutrophils) and greatly increases the risk for preterm labor, stillbirth, or neonatal GBS infection. The advent of animal models of chorioamnionitis provides a powerful tool to study host-pathogen relationships in vivo and ex vivo. The purpose of this study was to evaluate the innate immune response elicited by GBS and evaluate how antimicrobial strategies elaborated by these innate immune cells affect bacteria. Our work using a mouse model of GBS ascending vaginal infection during pregnancy reveals that clinically isolated GBS has the capacity to invade reproductive tissues and elicit host immune responses including infiltration of PMNs within the choriodecidua and placenta during infection, mirroring the human condition. Upon interacting with GBS, murine neutrophils elaborate DNA-containing extracellular traps, which immobilize GBS and are studded with antimicrobial molecules including lactoferrin. Exposure of GBS to holo- or apo-forms of lactoferrin reveals that the iron-sequestration activity of lactoferrin represses GBS growth and viability in a dose-dependent manner. Together, these data indicate that the mouse model of ascending infection is a useful tool to recapitulate human models of GBS infection during pregnancy. Furthermore, this work reveals that neutrophil extracellular traps ensnare GBS and repress bacterial growth via deposition of antimicrobial molecules, which drive nutritional immunity via metal sequestration strategies.

Lactoferrin from Camelus dromedarius Inhibits Nuclear Transcription Factor-kappa B Activation, Cyclooxygenase-2 Expression and Prostaglandin E2 Production in Stimulated Human Chondrocytes

Background:

Osteoarthritis (OA) is a progressive joint disorder, which remains the leading cause of chronic disability in aged people. Nuclear factor-kappa B (NF)-κB is a major cellular event in OA and its activation by interleukin-1β (IL-1β) plays a critical role in cartilage breakdown in these patients.

Objective:

In this study, we examined the effect of lactoferrin on NF-κB activation, cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE₂) production in stimulated human articular chondrocytes.

Materials and Methods:

Human chondrocytes were derived from OA articular cartilage and treated with camel lactoferrin and then stimulated with IL-1β. Gene expression was determined by TaqMan assays and protein expression was studied by Western immunoblotting. NF-κB activity and PGE₂ levels were determined by ELISA based assays. NF-κB activity was also determined by treatment of chondrocytes with NF-κB specific inhibitor Bay 11–7082.

Results:

Lactoferrin inhibited IL-1β-induced activation and nuclear translocation of NF-κB p65 in human OA chondrocytes. Lactoferrin also inhibited mRNA/protein expression of COX-2 and production of PGE₂. Moreover, Bay 11–7082 also inhibited IL-1β-induced expression of COX-2 and production of PGE₂. The inhibitory effect of lactoferrin on the IL-1β induced expression of COX-2 or production of PGE₂ was mediated at least in part via suppression of NF-κB activation.

Conclusions:

Our data determine camel lactoferrin as a novel inhibitor of IL-1β-induced activation of NF-κB signaling events and production of cartilage-degrading molecule PGE₂ via inhibition of COX-2 expressions. These results may have important implications for the development of novel therapeutic strategies for the prevention/treatment of OA and other degenerative/inflammatory diseases.

SUMMARY

Lactoferrin shows anti-arthritic activity in IL-1β stimulated primary human chondrocytes.

Lactoferrin inhibits IL-1β-induced NF-κB activation.

Lactoferrin inhibits production of cartilage degrading PGE2 via inhibition of COX-2 expression.

Abbreviations Used: OA: Osteoarthritis IL-1β: Interleukin-1 beta NF-κB: Nuclear factor-kappa B COX-2: cyclooxygenase-2 PGE₂: prostaglandin E₂

Lactoferrin Is an Allosteric Enhancer of the Proteolytic Activity of Cathepsin G

Protease-mediated degradation of proteins is critical in a plethora of physiological processes. Neutrophils secrete serine proteases including cathepsin G (CatG), neutrophile elastase (NE), and proteinase 3 (PR3) together with lactoferrin (LF) as a first cellular immune response against pathogens. Here, we demonstrate that LF increases the catalytic activity of CatG at physiological concentration, with its highest enhancing capacity under acidic (pH 5.0) conditions, and broadens the substrate selectivity of CatG. On a functional level, the enzymatic activity of CatG was increased in the presence of LF in granulocyte-derived supernatant. Furthermore, LF enhanced CatG-induced activation of platelets as determined by cell surface expression of CD62P. Consequently, LF-mediated enhancement of CatG activity might promote innate immunity during acute inflammation.

Nuclear factor (NF)-κB and its associated pathways are major molecular regulators of blood-induced joint damage in a murine model of hemophilia

BACKGROUND

The present study was designed to investigate the molecular signaling events from onset of bleeding through the development of arthropathy in a murine model of hemophilia A.

METHODS AND RESULTS

A sharp-injury model of hemarthrosis was used. A global gene expression array on joint-specific RNA isolated 3 h post-injury revealed nuclear factor-kappa B (NF-κB) as the major transcription factor triggering inflammation. As a number of genes encoding the cytokines, growth factors and hypoxia regulating factors are known to be activated by NF-κB and many of these are part of the pathogenesis of various joint diseases, we reasoned that NF-κB-associated pathways may play a crucial role in blood-induced joint damage. To further understand its role, we screened NF-κB-associated pathways between 1 h to 90 days after injury. After a single articular bleed, distinct members of the NF-κB family (NF-κB1/NF-κB2/RelA/RelB) and their responsive pro-inflammatory cytokines (IL-1β/IL-6/IFNγ/TNFα) were significantly up-regulated (> 2 fold, P < 0.05) in injured vs. control joints at the various time-points analyzed (1 h/3 h/7 h/24 h). After multiple bleeds (days 30/60/75/90), there was increased expression of NF-κB-associated factors that contribute to hypoxia (HIF-1α, 3.3-6.5 fold), angiogenesis (VEGF-α, 2.5-4.4 fold) and chondrocyte damage (matrix metalloproteinase-13, 2.8-3.8 fold) in the injured joints. Micro RNAs (miR) that are known to regulate NF-κB activation (miRs-9 and 155), inflammation (miRs-16, 155 and 182) and apoptosis (miRs-19a, 155 and 186) were also differentially expressed (-4 to +13-fold) after joint bleeding, indicating that the small RNAs could modulate the arthropathy phenotype.

CONCLUSIONS

These data suggest that NF-κB-associated signaling pathways are involved in the development of hemophilic arthropathy.

Six-transmembrane epithelial antigen of prostate 4 and neutrophil gelatinase-associated lipocalin expression in visceral adipose tissue is related to iron status and inflammation in human obesity

PURPOSE

Six-transmembrane epithelial antigen of prostate (STEAP)-4 and neutrophil gelatinase-associated lipocalin (NGAL) are novel adipokines related to iron homeostasis with potential roles in insulin resistance and inflammation. The aim of the present work was to evaluate the effect of obesity and iron status on gene expression levels of STEAP-4 and NGAL in visceral adipose tissue (VAT) and its implication in inflammation.

METHODS

VAT biopsies obtained from 53 subjects were used in the study. Real-time PCR and Western-blot were performed to quantify the levels of STEAP4 and NGAL in VAT as well as the association with other genes implicated in inflammatory pathways. Circulating ferritin and free iron concentrations were also determined.

RESULTS

Obese patients exhibited significantly increased STEAP4 and NGAL mRNA expression levels (P < 0.001) compared to lean subjects. Protein expression levels of NGAL (P < 0.05) and STEAP4 were also higher in the visceral fat depot of obese patients, although protein levels of STEAP4 did not reach statistical significance. A negative correlation (P < 0.05) between free iron concentrations and gene expression levels of both STEAP4 and NGAL was found, while circulating ferritin concentrations were positively correlated (P < 0.05) with NGAL mRNA after body fat (BF) adjustment. Furthermore, a significant positive association between STEAP4 and NGAL gene expression levels with inflammatory markers was also detected (P < 0.01).

CONCLUSION

These findings represent the first observation that STEAP4 and NGAL mRNA and protein levels in human VAT are related to iron status. Moreover, STEAP4 and NGAL are associated with pro-inflammatory markers suggesting their potential involvement in the low-grade chronic inflammation accompanying obesity.

Iron overload in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a major causative agent of chronic liver disease worldwide, but the actual mechanisms responsible for liver injury remain unclear. NAFLD includes a spectrum of clinical entities ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with possible evolution to cirrhosis and hepatocellular carcinoma. Iron is considered a putative element that interacts with oxygen radicals in inducing liver damage/fibrosis and insulin resistance. The role of hepatic iron in the progression of NASH remains controversial, but in some patients, iron may have a role in the pathogenesis of NASH. Though genetic factors, insulin resistance, dysregulation of iron-regulatory molecules, erythrophagocytosis by Kupffer cells may be responsible for hepatic iron accumulation in NASH, exact mechanisms involved in iron overload remain to be clarified. Iron reduction therapy such as phlebotomy or iron-restricted diet may be promising in patients with NAFLD/NASH to reduce hepatic injury as well as insulin resistance. Larger controlled trials of longer duration are warranted to assess the long-term clinical benefit of phlebotomy and/or iron-restricted diet in NAFLD/NASH.

Lactoferrin inhibits neutrophil apoptosis via blockade of proximal apoptotic signaling events

Neutrophils are the most abundant leukocyte and have a short lifespan, dying by apoptosis approximately five days after leaving the bone marrow. Their apoptosis can be delayed at sites of inflammation to extend their functional lifespan, but inappropriate inhibition of apoptosis contributes to chronic inflammatory disease. Levels of the physiological iron chelator lactoferrin are raised at sites of inflammation and we have shown previously that iron-unsaturated lactoferrin inhibited human neutrophil apoptosis, but the mechanisms involved were not determined. Here we report that the anti-apoptotic effect of lactoferrin is dependent upon its iron saturation status as iron-saturated lactoferrin did not affect neutrophil apoptosis. We also show that the effect of lactoferrin is mediated at an early stage in apoptosis as it inhibited activation of sphingomyelinase, generation of ceramide, activation of caspase 8 and Bax and cleavage of Bid. Lactoferrin did not inhibit apoptosis induced by exogenous ceramide, supporting the proposal that it acts upstream of ceramide generation. We therefore conclude that raised lactoferrin levels are likely to contribute to chronic inflammation by delaying neutrophil apoptosis and that this is achieved by inhibiting proximal apoptotic signaling events.

Signal transduction and metabolism in chondrocytes is modulated by lactoferrin

OBJECTIVE

Activation of granulocytes causes a considerable rise in the concentration of lactoferrin (Lf) in synovial fluid (SF). We here investigate consequences thereof on signal transduction and the balance between catabolic and anabolic metabolism in chondrocytes.

METHODS

Signal transduction was analysed in cultured chondrocytes by immunodetection of mitogen activated protein kinases (MAPK) and analysis of Smad2 translocation to the nucleus. Expression levels of matrix metalloproteinases (MMPs) and of aggrecan were measured by reverse-transcription-PCR. The proteolytic activity of MMPs was ascertained by zymography. Expression of the low-density-lipoprotein-receptor-related-protein-1 (LRP-1), a Lf receptor for signalling, was assayed by immunohistochemistry in cartilage and in cultured chondrocytes by immunoblotting.

RESULTS

We found LRP-1 expressed in dedifferentiated chondrocytes in culture and in cartilage tissue preferentially on the articular surface where it can encounter Lf within SF. Lf stimulated proliferation of chondrocytes, comparable to transforming growth factor-beta1 (TGFbeta1) and activated p38 and the extracellular-signal regulated-kinases 1/2 (ERK1/2) within minutes. Surprisingly, Lf induced nuclear Smad2 translocation, a signal pathway ascribed to TGFbeta receptor activation. Lf significantly increased the levels of catabolic indicators such as MMP1, MMP2, MMP3 and MMP13 and inhibited aggrecan synthesis.

CONCLUSION

Lf is a robust regulator of chondrocyte metabolism, comparable to TGFbeta1. The catabolic influence together with the proliferative stimulus indicates a function as an early phase cytokine, enhancing MMPs, necessary for degradation of damaged tissue and stimulating proliferation of chondrocytes, necessary for reconstruction.

Iron homoeostasis in rheumatic disease

Iron is critical in nearly all cell functions and the ability of a cell, tissue and organism to procure this metal is obligatory for survival. Iron is necessary for normal immune function, and relative iron deficiency is associated with mild immunosuppression. Concentrations of this metal in excess of those required for function can present both an oxidative stress and elevate risks for infection. As a result, the human has evolved to have a complex mechanism of regulating iron and limiting its availability. This homoeostasis can be disrupted. Autoimmune diseases and gout often present with abnormal iron homoeostasis, thus supporting a participation of the metal in these injuries. We review the role of iron in normal immune function and discuss both clinical evidence of altered iron homoeostasis in autoimmune diseases and gout as well as possible implications of both depletion and supplementation of this metal in this patient population. We conclude that altered iron homoeostasis may represent a purposeful response to inflammation that could have theoretical anti-inflammatory benefits. We encourage physicians to avoid routine iron supplementation in those without depleted iron stores.

Lactoferrin is a survival factor for neutrophils in rheumatoid synovial fluid

OBJECTIVES

Lactoferrin is an iron-binding protein that is released from activated neutrophils at sites of inflammation and has anti-microbial as well as anti-inflammatory properties. This study set out to determine whether lactoferrin can delay neutrophil apoptosis and could act as a survival factor for neutrophils in SF.

METHODS

Human peripheral blood and SF neutrophils were incubated with iron-free lactoferrin and apoptosis determined after 9 h. SF from patients with RA was added to isolated neutrophils, with or without immunodepletion of lactoferrin, and effects on neutrophil apoptosis determined. Levels of lactoferrin in SF were assessed and related to disease duration and markers of disease activity.

RESULTS

Iron-free lactoferrin significantly delayed apoptosis of peripheral blood neutrophils, in a concentration-dependent manner after 9 h in culture (P < 0.04). Lactoferrin could also delay apoptosis of neutrophils isolated from SF of patients with RA. SF from patients with established RA delayed apoptosis of peripheral blood neutrophils and this effect was significantly reduced by depletion of lactoferrin (P < 0.03). Lactoferrin levels in SF from patients with established RA did not correlate with disease severity, but did correlate with markers of inflammation (CRP) and with the presence of RF. SF from patients with arthritis of <12 weeks duration did not contain significant levels of lactoferrin.

CONCLUSION

Lactoferrin contributes to extended neutrophil survival in the rheumatoid joint in the established phase of RA but not in very early arthritis.

Iron stimulates urokinase plasminogen activator expression and activates NF-kappa B in human prostate cancer cells

Urokinase-type plasminogen activator (uPA) on prostate cancer cell surfaces mediates pericellular proteolysis and destruction of extracellular matrix barriers to tumor invasion and metastasis. Increased expression of tumor-associated uPA leads to enhanced tumor dissemination and poor cancer outcomes in men with prostate cancer. Expression of uPA is regulated in part by the oxidant-sensitive transcription factor, NF-kappa B (NF-kappaB), which is activated by intracellular reactive oxygen intermediates (ROI). This study examined the effect of iron on the production of ROI, activation of NF-kappaB and expression of uPA in the human prostate cancer cell line, PC-3. Treatment of PC-3 cells with iron in the form of ferric nitrilotriacetate (FeNTA) in the absence of added transferrin resulted in a dose-dependent increase in cellular ferritin content in both the presence and absence of neutralizing antibody to the transferrin receptor. Cellular uptake of iron resulted in stimulation of intracellular ROI production, and increases in uPA mRNA, antigen, and activity. Concurrent treatment with the iron chelator, desferrioxamine (DFO) abrogated these effects, and treatment with DFO alone inhibited constitutive uPA production. Finally, we observed nuclear translocation, and therefore activation of NF-kappaB in response to iron exposure. We conclude that iron enters PC-3 cells via a non-transferrin dependent pathway and increases uPA expression. Our data indicate that one mechanism by which iron may stimulate uPA production is through the generation of intracellular ROI and activation of NF-kappaB-mediated signaling pathways.

Cross-talk between iron metabolism and diabetes

Emerging scientific evidence has disclosed unsuspected influences between iron metabolism and type 2 diabetes. The relationship is bi-directional--iron affects glucose metabolism, and glucose metabolism impinges on several iron metabolic pathways. Oxidative stress and inflammatory cytokines influence these relationships, amplifying and potentiating the initiated events. The clinical impact of these interactions depends on both the genetic predisposition and the time frame in which this network of closely related signals acts. In recent years, increased iron stores have been found to predict the development of type 2 diabetes while iron depletion was protective. Iron-induced damage might also modulate the development of chronic diabetes complications. Iron depletion has been demonstrated to be beneficial in coronary artery responses, endothelial dysfunction, insulin secretion, insulin action, and metabolic control in type 2 diabetes. Here, we show that iron modulates insulin action in healthy individuals and in patients with type 2 diabetes. The extent of this influence should be tested in large-scale clinical trials, searching for the usefulness and cost-effectiveness of therapeutic measures that decrease iron toxicity. The study of individual susceptibility and of the mechanisms that influence tissue iron deposition and damage are proposed to be valuable in anticipating and treating diabetes complications.

A review of fluorescence methods for assessing labile iron in cells and biological fluids

A variety of biochemical, pharmacological, and toxicological properties have been attributed to labile forms of iron that are associated with cells or with biological fluids. Unlike the major fraction of bioiron which is protein bound, the labile bioiron is chelatable and therefore amenable for detection by metal-sensing devices that are coupled to chelation moieties. The present review deals with the detection of various labile forms of iron present in living cells and in fluids of biological interest, in health and disease. The main focus of the review is on the design and application of fluorescent probes as analytical tools for assessing labile iron and iron transport mechanisms and the efficiency of iron chelators in solution and in cellular systems.

Enhanced Th1 response to Staphylococcus aureus infection in human lactoferrin-transgenic mice

Lactoferrin (Lf) is an iron-binding protein of external secretions and neutrophil secondary granules with antimicrobial and immunomodulatory activities. To further define these properties of Lf, we have investigated the response to Staphylococcus aureus infection in transgenic mice carrying a functional human Lf gene. The transgenic mice cleared bacteria significantly better than congenic littermates, associated with a trend to reduced incidence of arthritis, septicemia, and mortality. We identified two pathways by which S. aureus clearance was enhanced. First, human Lf directly inhibited the growth of S. aureus LS-1 in vitro. Second, S. aureus-infected transgenic mice exhibited enhanced Th1 immune polarization. Thus, spleen cells from infected transgenic mice produced higher levels of TNF-alpha and IFN-gamma and less IL-5 and IL-10 upon stimulation ex vivo with the exotoxin toxic shock syndrome toxin-1 compared with congenic controls. To confirm that these effects of Lf transgene expression could occur in the absence of live bacterial infection, we also showed that Lf-transgenic DBA/1 mice exhibited enhanced severity of collagen-induced arthritis, an established model of Th1-induced articular inflammation. Higher levels of stainable iron in the spleens of transgenic mice correlated with human Lf distribution, but all other parameters of iron metabolism did not differ between transgenic mice and wild-type littermates. These results demonstrate that human Lf can mediate both antimicrobial and immunomodulatory activities with downstream effects on the outcome of immune pathology in infectious and inflammatory disease.

Effect of oral iron supplementation on oxidative stress and colonic inflammation in rats with induced colitis

BACKGROUND

Iron supplementation may increase disease activity in ulcerative colitis, possibly through the production of reactive oxygen species from the Fenton reaction.

AIM

To assess the effects of two doses of oral iron on intestinal inflammation and oxidative stress in experimental colitis.

METHODS

Colitis was induced in rats by giving 5% dextran sulphate sodium in drinking water for 7 days. First, using a 2 x 2 factorial design, rats with or without dextran sulphate sodium received the regular diet or a diet containing iron 3%/kg diet. Second, rats with dextran sulphate sodium-induced colitis were supplemented with iron 0.3%/kg diet and compared with rats on dextran sulphate sodium and regular diet. The body weight change, histological scores, colon length, rectal bleeding, plasma and colonic lipid peroxides, colonic glutathione peroxidase and plasma vitamin E and C were measured. Faecal analysis for haem and total, free and ethylenediaminetetra-acetic acid-chelatable iron was also performed.

RESULTS

Iron 3% and iron 0.3% increased the activity of dextran sulphate sodium-induced colitis, as demonstrated by higher histological scores, heavier rectal bleeding and further shortening of the colon. This was associated with increased lipid peroxidation and decreased antioxidant vitamins. Faecal iron available to the Fenton reaction was increased in a dose-dependent manner.

CONCLUSIONS

Iron supplementation taken orally enhanced the activity of dextran sulphate sodium-induced colitis and is associated with an increase in oxidative stress.

Human lactoferrin: a novel therapeutic with broad spectrum potential

Lactoferrin (Lf), a natural defence iron-binding protein, has been found to possess antibacterial, antimycotic, antiviral, antineoplastic and anti-inflammatory activity. The protein is present in exocrine secretions that are commonly exposed to normal flora: milk, tears, nasal exudate, saliva, bronchial mucus, gastrointestinal fluids, cervico-vaginal mucus and seminal fluid. Additionally, Lf is a major constituent of the secondary specific granules of circulating polymorphonuclear neutrophils (PMNs). The apoprotein is released on degranulation of the PMNs in septic areas. A principal function of Lf is that of scavenging free iron in fluids and inflamed areas so as to suppress free radical-mediated damage and decrease the availability of the metal to invading microbial and neoplastic cells. Mechanisms of action of Lf in addition to iron deprivation are also described. Administration of exogenous human or bovine Lf to hosts with various infected or inflamed sites has resulted in some prophylactic or therapeutic effects. However, an adverse response to the protein might occur if it were to stimulate antibody production or if it were to provide iron to the invading pathogen. The recombinant form of human Lf has become available and development of the product for use in a wide range of medical conditions can now be anticipated.

A role for IL-18 in neutrophil activation

IL-18 expression and functional activity has been identified in several autoimmune and infectious diseases. To clarify the potential role of IL-18 during early innate immune responses, we have explored the capacity of IL-18 to activate neutrophils. Human peripheral blood-derived neutrophils constitutively expressed IL-18R (alpha and beta) commensurate with the capacity to rapidly respond to IL-18. IL-18 induced cytokine and chemokine release from neutrophils that was protein synthesis dependent, up-regulated CD11b expression, induced granule release, and enhanced the respiratory burst following exposure to fMLP, but had no effect upon the rate of neutrophil apoptosis. The capacity to release cytokine and chemokine was significantly enhanced in neutrophils derived from rheumatoid arthritis synovial fluid, indicating differential responsiveness to IL-18 dependent upon prior neutrophil activation in vivo. Finally, IL-18 administration promoted neutrophil accumulation in vivo, whereas IL-18 neutralization suppressed the severity of footpad inflammation following carrageenan injection. The latter was accompanied by reduction in tissue myeloperoxidase expression and suppressed local TNF-alpha production. Together, these data define a novel role for IL-18 in activating neutrophils and thereby promoting early innate immune responses.

In vitro study of the antioxidant properties of nimesulide and 4-OH nimesulide: effects on HRP- and luminol-dependent chemiluminescence produced by human chondrocytes

OBJECTIVES

Reactive oxygen species (ROS) are now recognized to play an important role in the pathogenesis of rheumatic diseases and constitute an interesting therapeutic target for drugs. This in vitro study was designed to evaluate the antioxidant properties of nimesulide (NIM), a nonsteroidal antiinflammatory drug of the sulfonanilide class, and its main metabolite 4-OH nimesulide (4-OHNIM).

METHODS

The scavenging effects of NIM and 4-OH NIM on hydroxyl radical ((.)OH) and superoxide anions (O(minusd)(2)) were investigated by electron spin resonance (ESR), using 5, 5-dimethylpyrroline-N-oxide (DMPO) as the spin trap agent. The quenching properties of these drugs on hypochlorite anion was studied by luminol enhanced chemiluminescence. Finally, the effects of NIM and 4-OHNIM on the reactive oxygen species production by human articular chondrocytes were recorded by HRP and luminol-enhanced chemiluminescence.

RESULTS

By this method it has been demonstrated that NIM and 4-OHNIM, at concentrations ranging from 10 to 100 microM, are potent scavengers of(.)OH whereas only 4-OHNIM was capable to scavenge O(minusd)(2). Chemiluminescence generated by HOCl was also significantly and dose-dependently inhibited by both NIM and 4-OHNIM. Nevertheless, at each concentration tested, the inhibitory effect of 4-OHNIM was significantly more marked, even at the highest concentration (100 microM). Furthermore, when chondrocytes were pre-incubated for 48-96 h with NIM or 4-OHNIM, the luminol- and HRP-dependent CL produced by the cells was significantly inhibited in a dose-dependent manner.

CONCLUSIONS

NIM and 4-OHNIM may protect cartilage against oxidative stress, not only by scavenging ROS but also by inhibiting their production by chondrocytes.

In vitro study of the antioxidant properties of non steroidal anti-inflammatory drugs by chemiluminescence and electron spin resonance (ESR)

OBJECTIVES

To determine the antioxidant activities of nonsteroidal anti-inflammatory drugs (NSAIDS), we examined by chemiluminescence (CL) and electron spin resonance (ESR) their scavenging properties towards lipid peroxides, hypochlorous acid and peroxynitrite.

METHODS

The antioxidant properties of nimesulide (NIM), 4-hydroxynimesulide (4-HONIM), aceclofenac (ACLO), 4-hydroxyaceclofenac (4-HOA-CLO), diclofenac (DICLO) and indomethacin (INDO) were tested on four different reactive oxygen species (ROS) generating systems: (I) phorbol-myristate acetate (PMA)-activated neutrophils, (II) Fe2+/ascorbate-induced lipid peroxidation, (III) HOCl-induced light emission, (IV) the kinetics of ONOO- decomposition followed by spectrophotometry. ROS production was monitored by luminol-enhanced CL or by ESR using two different spin traps.

RESULTS

At 10 microM, ACLO, NIM, 4-HONIM, 4-HOA-CLO, and DICLO decreased luminol-enhanced CL generated by PMA-activated neutrophils. Inversely, INDO increased the luminol enhanced CL. Interestingly, hydroxylated metabolites were more potent antioxidants than the parent drugs. Furthermore, all drugs tested, excepted ACLO, lowered lipid peroxidation induced by Fe2+/ascorbate system. ACLO and DICLO, even at the highest concentration tested (100 microM), did not significantly lower HOCl induced CL, whereas the other drugs were potent scavengers. Finally, all the NSAIDS accelerated decomposition of ONOO-, suggesting a potential capacity of the molecules to scavenge peroxynitrite.

CONCLUSION

The NSAIDs possess variable degrees of antioxidant activities, linked to their ability to react with HOCl, lipid peroxides or ONOO-. These antioxidant activities could offer interesting targeted side-effects in the treatment of joint inflammatory diseases.

Inhibition of binding of lactoferrin to the human promonocyte cell line THP-1 by heparin: the role of cell surface sulphated molecules

Lactoferrin, an iron-binding protein of the transferrin family, is a highly basic protein which interacts with many acidic molecules, including heparin proteoglycans. Such interactions may modify some of the biological properties of lactoferrin. In the present work we found that heparin caused a dose-dependent inhibition of specific binding of both human and bovine lactoferrin to human monocytic THP-1 cells. Low-affinity binding sites (Kd 500 nM) were more susceptible to inhibition by heparin than the high-affinity sites (Kd 100 nM). The effect was mediated by interaction between lactoferrin and heparin rather than by competition between heparin and lactoferrin for common binding sites on the cells. Pretreatment of cells with NaClO3 to prevent sulphation of surface glycosaminoglycans reduced lactoferrin binding, and de-N-sulphated heparin did not inhibit binding of lactoferrin to THP-1 cells. These results suggest that heparin binding and monocyte/macrophage binding by lactoferrin both involve interactions between basic regions in the N1 domain of lactoferrin and sulphate groups. The N-terminal Arg2-Arg5 sequence of human lactoferrin may be involved, but it does not seem to be the key element in these interactions.

Presence of bleomycin-detectable free iron in the alveolar system of preterm infants

Chronic lung disease (CLD) is a major cause of long term morbidity in preterm infants. Reactive oxygen species (ROS) play an important role in the pathogenesis of CLD. We show that a high percentage (63 to 83%) of the investigated bronchoalveolar secretions (BAS) of neonates contain bleomycin-detectable free iron concentrations (0. 04-0.124 nmol/micrograms SC, median range). Beside the presence of redox-active iron several iron-binding proteins like transferrin, ferritin and lactoferrin were determined in BAS. Comparison of protein distribution within the first three days of life showed slight differences between the group of preterm infants who developed CLD and the neonates who recovered from RDS. Because of the existence of free iron we suggest a higher risk of hydroxyl radical formation in the alveolar space. In an artificial system with addition of iron and hydrogen peroxide we were able to demonstrate OH-radical production in BAS by electron paramagnetic resonance (EPR). OH-radical formation by H2O2 and iron in buffer solution was slightly enhanced in the presence of BAS, indicating the absence of OH-radical-scavengers in BAS.

Iron loading and disease surveillance

Iron is an oxidant as well as a nutrient for invading microbial and neoplastic cells. Excessive iron in specific tissues and cells (iron loading) promotes development of infection, neoplasia, cardiomyopathy, arthropathy, and various endocrine and possibly neurodegenerative disorders. To contain and detoxify the metal, hosts have evolved an iron withholding defense system, but the system can be compromised by numerous factors. An array of behavioral, medical, and immunologic methods are in place or in development to strengthen iron withholding. Routine screening for iron loading could provide valuable information in epidemiologic, diagnostic, prophylactic, and therapeutic studies of emerging infectious diseases.