Inflammation-induced effects on iron-related proteins in splenic macrophages and the liver in mice

Liver iron stores and effectors of ferroptosis are dependent on age and sex

Ferroptosis is a form of cell death characterized by a pro-oxidative cellular milieu and iron-dependent lipid peroxidation. Ferroptosis has been implicated in various forms of liver injury, in keeping with the major role of the liver in iron metabolism. Limited research has addressed potential differences in ferroptosis mediators with age and sex, especially in an in vivo model. The goal of this investigation was to evaluate hepatic labile iron and mediators of ferroptosis with ageing in both sexes. Because female animals generally display greater antioxidant defences than males, we hypothesized that females would display a phenotype resistant to ferroptosis. Here, we determined iron contents, protein expression of ferroptosis mediators and measures of oxidative injury in liver samples from 12- and 24-month-old male and female Fischer 344 rats. In comparison to males, the livers of female rats at both ages contained more non-haem iron, which was associated with greater ferritin heavy chain expression and attenuated expression of transferrin receptor-1. In female rats, the 24-month-old group had higher contents of thiobarbituric acid reactive substances compared with their 12-month-old counterparts, yet similar contents of labile iron. These results suggest a disconnect between labile iron contents and oxidative injury with age. Female animals also displayed greater expression of acyl-CoA synthetase long-chain family member 4 (ACSL4), a modulator of ferroptosis, and greater abundance of high molecular weight 4-hydroxnonenal-modified proteins. These results demonstrate clear differences in iron and ferroptosis mediators between sexes and suggest that female rats of this strain might be more susceptible to ferroptosis.

Review of the role of the endogenous opioid and melanocortin systems in the restless legs syndrome

Restless legs syndrome (RLS) is responsive to opioid, dopaminergic and iron-based treatments. Receptor blocker studies in RLS patients suggest that the therapeutic efficacy of opioids is specific to the opioid receptor and mediated indirectly through the dopaminergic system. An RLS autopsy study reveals decreases in endogenous opioids, β-endorphin and perhaps Met-enkephalin in the thalamus of RLS patients. A total opioid receptor knock-out (mu, delta and kappa) and a mu-opioid receptor knock-out mouse model of RLS show circadian motor changes akin to RLS and, although both models show sensory changes, the mu-opioid receptor knock mouse shows circadian sensory changes closest to those seen in idiopathic RLS. Both models show changes in striatal dopamine, anaemia and low serum iron. However, only in the total receptor knock-out mouse do we see the decreases in serum ferritin that are normally found in RLS. There are also decreases in serum iron when wild-type mice are administered a mu-opioid receptor blocker. In addition, the mu-opioid receptor knock-out mouse also shows increases in striatal zinc paralleling similar changes in RLS. Adrenocorticotropic hormone and α-melanocyte stimulating hormone are derived from pro-opiomelanocortin as is β-endorphin. However, they cause RLS-like symptoms and periodic limb movements when injected intraventricularly into rats. These results collectively suggest that an endogenous opioid deficiency is pathogenetic to RLS and that an altered melanocortin system may be causal to RLS as well.

TFR1 expression in induced sputum is associated with asthma severity

Background

Asthma is characterized as a chronic inflammatory airway disease. Iron accumulation is related to asthma pathogenesis. Transferrin receptor 1(TFR1) expression is associated with intracellular iron overload in macrophages. In our study, we explored the association among TFR1 expression, the inflammatory macrophage phenotype, and asthma severity.

Methods

Induced sputum was collected from 50 asthma patients. Real-time PCR was used to evaluate mRNA expression. The status of inflammatory macrophage phenotype was assessed using flow cytometry.

Results

TFR1 levels were inversely correlated with forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC) and FEV₁/vital capacity (VC). Among inflammatory cytokines, TFR1 expression was positively correlated with IL-1β, TNF-α, IL-6, IFN-γ, and IL-17A mRNA expression in induced sputum. Moreover, TFR1 expression was positively correlated with the number of proinflammatory M1 macrophages and iNOS expression in induced sputum. Neutrophil counts in induced sputum were significantly and positively related to TFR1 expression. Furthermore, TFR1 expression showed an increasing trend in asthma patients with no family history. Our findings indicated that TFR1 expression was consistent with the asthma severity index, especially the proinflammatory M1 macrophage phenotype. TFR1 expression may be a good marker to indicate asthma severity.

Modelling Systemic Iron Regulation during Dietary Iron Overload and Acute Inflammation: Role of Hepcidin-Independent Mechanisms

Systemic iron levels must be maintained in physiological concentrations to prevent diseases associated with iron deficiency or iron overload. A key role in this process plays ferroportin, the only known mammalian transmembrane iron exporter, which releases iron from duodenal enterocytes, hepatocytes, or iron-recycling macrophages into the blood stream. Ferroportin expression is tightly controlled by transcriptional and post-transcriptional mechanisms in response to hypoxia, iron deficiency, heme iron and inflammatory cues by cell-autonomous and systemic mechanisms. At the systemic level, the iron-regulatory hormone hepcidin is released from the liver in response to these cues, binds to ferroportin and triggers its degradation. The relative importance of individual ferroportin control mechanisms and their interplay at the systemic level is incompletely understood. Here, we built a mathematical model of systemic iron regulation. It incorporates the dynamics of organ iron pools as well as regulation by the hepcidin/ferroportin system. We calibrated and validated the model with time-resolved measurements of iron responses in mice challenged with dietary iron overload and/or inflammation. The model demonstrates that inflammation mainly reduces the amount of iron in the blood stream by reducing intracellular ferroportin transcription, and not by hepcidin-dependent ferroportin protein destabilization. In contrast, ferroportin regulation by hepcidin is the predominant mechanism of iron homeostasis in response to changing iron diets for a big range of dietary iron contents. The model further reveals that additional homeostasis mechanisms must be taken into account at very high dietary iron levels, including the saturation of intestinal uptake of nutritional iron and the uptake of circulating, non-transferrin-bound iron, into liver. Taken together, our model quantitatively describes systemic iron metabolism and generated experimentally testable predictions for additional ferroportin-independent homeostasis mechanisms.

The importance of iron in many physiological processes relies on its ability to participate in reduction-oxidation reactions. This property also leads to potential toxicity if concentrations of free iron are not properly managed by cells and tissues. Multicellular organisms therefore evolved intricate regulatory mechanisms to control systemic iron levels. A central regulatory mechanism is the binding of the hormone hepcidin to the iron exporter ferroportin, which controls the major fluxes of iron into blood plasma. Here, we present a mathematical model that is fitted and validated against experimental data to simulate the iron content in different organs following dietary changes and/or inflammatory states, or genetic perturbation of the hepcidin/ferroportin regulatory system. We find that hepcidin mediated ferroportin control is essential, but not sufficient to quantitatively explain several of our experimental findings. Thus, further regulatory mechanisms had to be included in the model to reproduce reduced serum iron levels in response to inflammation, the preferential accumulation of iron in the liver in the case of iron overload, or the maintenance of physiological serum iron concentrations if dietary iron levels are very high. We conclude that hepcidin-independent mechanisms play an important role in maintaining systemic iron homeostasis.

Hepcidin inhibits Smad3 phosphorylation in hepatic stellate cells by impeding ferroportin-mediated regulation of Akt

Hepatic stellate cell (HSC) activation on liver injury facilitates fibrosis. Hepatokines affecting HSCs are largely unknown. Here we show that hepcidin inhibits HSC activation and ameliorates liver fibrosis. We observe that hepcidin levels are inversely correlated with exacerbation of fibrosis in patients, and also confirm the relationship in animal models. Adenoviral delivery of hepcidin to mice attenuates liver fibrosis induced by CCl₄ treatment or bile duct ligation. In cell-based assays, either hepcidin from hepatocytes or exogenous hepcidin suppresses HSC activation by inhibiting TGFβ1-mediated Smad3 phosphorylation via Akt. In activated HSCs, ferroportin is upregulated, which can be prevented by hepcidin treatment. Similarly, ferroportin knockdown in HSCs prohibits TGFβ1-inducible Smad3 phosphorylation and increases Akt phosphorylation, whereas ferroportin over-expression has the opposite effect. HSC-specific ferroportin deletion also ameliorates liver fibrosis. In summary, hepcidin suppresses liver fibrosis by impeding TGFβ1-induced Smad3 phosphorylation in HSCs, which depends on Akt activated by a deficiency of ferroportin.

The peptide hormone hepcidin is released from hepatocytes and regulates iron homoeostasis. Here, the authors show that hepcidin also regulates the activation of hepatic stellate cells (HSCs) in mouse models of liver fibrosis by reducing ferroportin expression and inhibiting the HSC response to TGFβ.

Effects of Il-33/St2 pathway on alteration of iron and hematological parameters in acute inflammation

AIM

The aim of this study was to examine the role of the IL-33/ST2 pathway in pathogenesis of acute inflammation by investigating its possible role in alteration of iron and hematological parameters in experimental model of acute inflammation.

MATERIAL AND METHODS

Wild-type and ST2 knockout BALB/c mice were divided into four groups: wild-type control group, ST2-/- control group, wild-type inflammatory group, and ST2-/- inflammatory group. Acute inflammation was induced by intramuscular injection of turpentine oil, while control groups were injected with saline. After 12h animals were anesthetized, and the treated tissue, blood and spleen were collected. Iron concentration in the treated tissue, hemoglobin blood concentration, mean corpuscular hemoglobin (MCH), hematocrit, erythrocyte, neutrophil and lymphocyte blood count, and erythrocytes percentage in spleen were determined.

RESULTS

Iron concentration in the treated tissue was significantly higher in wild-type inflammatory group (WT-I) when compared to both, the wild-type control group (WT-C) and ST2-/- inflammatory group (KO-I). There was no significant difference in iron concentration between ST2-/- control group (KO-C) and the KO-I. MCH had significantly decreased in WT-I when compared to WT-C, while there was no significant difference between KO-C and KO-I. Hemoglobin blood concentration significantly increased in KO-I in comparison to KO-C, while it did not significantly differ between WT-I and KO-I. Erythrocyte count and hematocrit had significantly increased, while the percentage of erythrocytes in spleen decreased in both inflammatory groups when compared to their controls. Neutrophil count significantly decreased in WT-I, when compared to WT-C. Lymphocyte count decreased in both inflammatory groups when compared to their controls.

CONCLUSION

Results of this study indicate that the IL-33/ST2 axis could have a role in the alteration of iron in acute inflammation, namely in an increase of iron concentration at the site of acute inflammation and a decrease of blood mean corpuscular hemoglobin.

Hemodialysis restored iron distribution that was sequestered in the spleen by bilateral nephrectomy

Acute kidney injury (AKI) is associated with dysregulated iron metabolism, which may play a significant role in cellular injury. The effect of hemodialysis (HD) on iron metabolism in AKI therapy has not been well defined. The effects of HD on iron parameters were tested in control rats and bilateral nephrectomy (BNx) rats. The BNx rats were divided into the following three groups: 1) the sham-operated group (BNx-Sham), 2) the BNx group, and 3) the HD group (BNx-HD), which received HD therapy 40–45 h after BNx. Sections of the liver or spleen were stained with Berlin blue to examine the accumulation of iron. The mRNA levels of hepcidin and ferroportin 1 in the spleen and liver were also quantified using RT-PCR. In the BNx group, the plasma iron and hematocrit levels were decreased, and hepcidin levels were increased. The iron staining in the spleen in the BNx group was significantly more intense than that in the BNx-Sham group; however, after an HD session, splenic iron staining diminished to the level of the sham group along with an increase in plasma iron and a decrease in hepcidin. BNx moved iron from hemoglobin and the plasma to the spleen, which is associated with an increase in plasma hepcidin. A single HD session accelerated the release of iron from the spleen, and the increased plasma iron was linked to the removal of hepcidin. Our data suggested that hepcidin might dynamically modulate the iron metabolism in BNx as well as in HD.

Altered expression of iron regulatory proteins with aging is associated with transient hepatic iron accumulation after environmental heat stress

An increasing body of evidence suggests that dysregulation of iron metabolism contributes to age-related pathologies. We have previously observed increased hepatic iron with aging, and that environmental heat stress stimulates a further increase in iron and oxidative liver injury in old rats. The purpose of this study was to determine a mechanism for the increase in hepatic iron in old rats after heat stress. Young (6 mo) and old (24 mo) Fischer 344 rats were exposed to two heating bouts separated by 24 h. Livers were harvested after the second heat stress, and protein levels of the iron import protein, transferrin receptor-1 (TFR1), and the iron export protein, ferroportin (Fpn) were determined by immunoblot. In the nonheated condition, old rats had lower TFR1 expression, and higher Fpn expression. After heat stress, TFR1 declined in the old rats, and iron chelation studies demonstrated that this decline was dependent on a hyperthermia-induced increase in iron. TFR1 did not change in the young rats after heat stress. Since TFR1 is inversely regulated by iron, our results suggest that the increase in intracellular iron with aging and heat stress lower TFR1 expression. Fpn expression increased in both age groups after heat stress, but this response was delayed in old rats. This delay in the induction of an iron exporter suggests a mechanism for the increase in hepatic iron and oxidative injury after heat stress in aged organisms.