Iron excretion in iron-overloaded rats following the change from an iron-loaded to an iron-deficient diet

Tetramethylpyrazine nitrone activates hypoxia-inducible factor and regulates iron homeostasis to improve renal anemia

Renal anemia is one of the most common complications of chronic kidney disease and diabetic kidney disease. Despite the progress made in recent years, there is still an urgent unmet clinical need for renal anemia treatment. In this research, we investigated the efficacy and mechanism of action of the novel tetramethylpyrazine nitrone (TBN). Animal models of anemia including the streptozotocin (STZ)-induced spontaneously hypertensive rats (SHR) and the cisplatin (CDDP)-induced C57BL/6J mice are established to study the TBN's effects on expression of hypoxia-inducible factor and erythropoietin. To explore the mechanism of TBN's therapeutic effect on renal anemia, cobalt chloride (CoCl2) is used in Hep3B/HepG2 cells to simulate a hypoxic environment. TBN is found to increase the expression of hypoxia-inducible factor HIF-1α and HIF-2α under hypoxic conditions and reverse the reduction of HIFs expression caused by saccharate ferric oxide (SFO). TBN also positively regulates the AMPK pathway. TBN stimulates nuclear transcription and translation of erythropoietin by enhancing the stability of HIF-1α expression. TBN has a significant regulatory effect on several major biomarkers of iron homeostasis, including ferritin, ferroportin (FPN), and divalent metal transporter-1 (DMT1). In conclusion, TBN regulates the AMPK/mTOR/4E-BP1/HIFs pathway, and activates the hypoxia-inducible factor and regulates iron homeostasis to improve renal anemia.

Gastrointestinal iron excretion and reversal of iron excess in a mouse model of inherited iron excess

The current paradigm in the field of mammalian iron biology states that body iron levels are determined by dietary iron absorption, not by iron excretion. Iron absorption is a highly regulated process influenced by iron levels and other factors. Iron excretion is believed to occur at a basal rate irrespective of iron levels and is associated with processes such as turnover of intestinal epithelium, blood loss, and exfoliation of dead skin. Here we explore iron excretion in a mouse model of iron excess due to inherited transferrin deficiency. Iron excess in this model is attributed to impaired regulation of iron absorption leading to excessive dietary iron uptake. Pharmacological correction of transferrin deficiency not only normalized iron absorption rates and halted progression of iron excess but also reversed body iron excess. Transferrin treatment did not alter the half-life of ⁵⁹Fe in mutant mice. ⁵⁹Fe-based studies indicated that most iron was excreted via the gastrointestinal tract and suggested that iron-loaded mutant mice had increased rates of iron excretion. Direct measurement of urinary iron levels agreed with ⁵⁹Fe-based predictions that urinary iron levels were increased in untreated mutant mice. Fecal ferritin levels were also increased in mutant mice relative to wild-type mice. Overall, these data suggest that mice have a significant capacity for iron excretion. We propose that further investigation into iron excretion is warranted in this and other models of perturbed iron homeostasis, as pharmacological targeting of iron excretion may represent a novel means of treatment for diseases of iron excess.

Disturbance of ion environment and immune regulation following biodistribution of magnetic iron oxide nanoparticles injected intravenously

Although it is expected that accumulation of metal oxide nanoparticles that can induce redox reaction in the biological system may influence ion homeostasis and immune regulation through generation of free radicals, the relationship is still unclear. In this study, mice received magnetic iron oxide nanoparticles (M-FeNPs, 2 and 4 mg/kg) a single via the tail vein, and their distribution in tissues was investigated over time (1, 4, and 13 weeks). In addition, we evaluated the effects on homeostasis of redox reaction-related elements, the ion environment and immune regulation. The iron level in tissues reached at the maximum on 4 weeks after injection and M-FeNPs the most distributed in the spleen at 13 weeks. Additionally, levels of redox reaction-related elements in tissues were notably altered since 1 week post-injection. While levels of K(+) and Na(+) in tissue tended to decrease with time, Ca(2+) levels reached to the maximum at 4 weeks post-injection. On 13 weeks post-injection, the increased percentages of neutrophils and eosinophils, the enhanced release of LDH, and the elevated secretion of IL-8 and IL-6 were clearly observed in the blood of M-FeNP-treated mice compared to the control. While expression of antigen presentation related-proteins and the maturation of dendritic cells were markedly inhibited following distribution of M-FeNPs, the expression of several chemokines, including CXCR2, CCR5, and CD123, was enhanced on the splenocytes of the treated groups. Taken together, we suggest that accumulation of M-FeNPs may induce adverse health effects by disturbing homeostasis of the immune regulation and ion environment.

Iron excretion in iron dextran-overloaded mice

BACKGROUND

Iron homeostasis in humans is tightly regulated by mechanisms aimed to conserve iron for reutilisation, with a negligible role played by excretory mechanisms. In a previous study we found that mice have an astonishing ability to tolerate very high doses of parenterally administered iron dextran. Whether this ability is linked to the existence of an excretory pathway remains to be ascertained.

MATERIALS AND METHODS

Iron overload was generated by intraperitoneal injections of iron dextran (1 g/kg) administered once a week for 8 weeks in two different mouse strains (C57bl/6 and B6D2F1). Urinary and faecal iron excretion was assessed by inductively coupling plasma-mass spectrometry, whereas cardiac and liver architecture was evaluated by echocardiography and histological methods. For both strains, 24-hour faeces and urine samples were collected and iron concentration was determined on days 0, 1 and 2 after iron administration.

RESULTS

In iron-overloaded C57bl/6 mice, the faecal iron concentration increased by 218% and 157% on days 1 and 2, respectively (p<0.01). The iron excreted represented a loss of 14% of total iron administered. Similar but smaller changes was also found in B6D2F1 mice. Conversely, we found no significant changes in the concentration of iron in the urine in either of the strains of mice. In both strains, histological examination showed accumulation of iron in the liver and heart which tended to decrease over time.

CONCLUSIONS

This study indicates that mice have a mechanism for removal of excess body iron and provides insights into the possible mechanisms of excretion.

Safety and efficacy of combined chelation therapy with deferasirox and deferoxamine in a gerbil model of iron overload

INTRODUCTION

Combined therapy with deferoxamine (DFO) and deferasirox (DFX) may be performed empirically when DFX monotherapy fails. Given the lack of published data on this therapy, the study goal was to assess the safety and efficacy of combined DFO/DFX therapy in a gerbil model.

METHODS

Thirty-two female Mongolian gerbils 8-10 weeks old were divided into 4 groups (sham chelated, DFO, DFX, DFO/DFX). Each received 10 weekly injections of 200 mg/kg iron dextran prior to initiation of 12 weeks of chelation. Experimental endpoints were heart and liver weights, iron concentration and histology.

RESULTS

In the heart, there was no significant difference among the treatment groups for wet-to-dry ratio, iron concentration and iron content. DFX-treated animals exhibited lower organ weights relative to sham-chelated animals (less iron-mediated hypertrophy). DFO-treated organs did not differ from sham-chelated organs in any aspects. DFX significantly cleared hepatic iron. No additive effects were observed in the organs of DFO/DFX-treated animals.

CONCLUSIONS

Combined DFO/DFX therapy produced no detectable additive effect above DFX monotherapy in either the liver or heart, suggesting competition with spontaneous iron elimination mechanisms for chelatable iron. Combined therapy was well tolerated, but its efficacy could not be proven due to limitations in the animal model.

Role of the kidney in iron homeostasis: renal expression of Prohepcidin, Ferroportin, and DMT1 in anemic mice

It is known that renal tissue plays a role in normal iron homeostasis. The current study examines kidney function in iron metabolism under hemolytic anemia studying renal expression of Prohepcidin, Ferroportin (MTP1), and divalent metal transporter 1 (DMT1). The relationship between these proteins and iron pigments was also investigated. Immunohistochemical procedures to study renal expression of Prohepcidin, MTP1, and DMT1 were performed in healthy and anemic mice. Renal tissue iron was determined by Prussian blue iron staining. To assess anemia evolution and erythropoietic recovery, we used conventional tests. In healthy mice, Prohepcidin expression was marked in proximal tubules and inner medulla and absent in outer medulla. Cortical tissue of healthy mice also showed MTP1 immunostaining, mainly in the S2 segment of proximal tubules. Medullar tissue showed MTP1 expression in the inner zone. In addition, S2 segments showed intense DMT1 immunoreactivity with homogeneous DMT1 distribution throughout renal medulla. The main cortical findings in hemolytic anemia were in S2 segments of proximal tubules where we found that decreased Prohepcidin expression coincided with an increment in Ferroportin and DMT1 expression. This expression pattern was concomitant with increased iron in the same tubular zone. However, in medullar tissue both Prohepcidin and MTP1 decreased and DMT1 was detected mainly in larger diameter tubules. Our findings clearly demonstrate that in hemolytic anemia, renal Prohepcidin acts in coordination with renal Ferroportin and DMT1, indicating the key involvement of kidney in iron homeostasis when iron demand is high. Further research is required to learn more about these regulatory mechanisms.

Tissue iron distribution and urinary mineral excretion vary depending on the form of iron (FeSO4 or NaFeEDTA) and the route of administration (oral or subcutaneous) in rats given high doses of iron

Sodium iron ethylenediaminetetraacetate (NaFeEDTA) has considerable promise as an iron fortificant in food. However, effects of administering high levels of NaFeEDTA on tissue iron distribution and mineral excretion are not well understood. The objectives of this study were to assess nonheme iron distribution in the body and urinary excretion of Ca, Mg, Cu, Fe, and Zn after daily administration of high levels of iron to rats over 21 days. Iron was either given orally with food or injected subcutaneously, as either FeSO 4 or NaFeEDTA. Selected tissues were collected for nonheme iron analysis. Estimated total body nonheme iron levels were similar in rats fed NaFeEDTA or FeSO 4, but the tissue distribution was different: it was 53% lower in the liver and 86% higher in the kidneys among rats fed NaFeEDTA than among those fed FeSO 4. In contrast, body nonheme iron was 3.2-fold higher in rats injected with FeSO 4 than in rats injected with NaFeEDTA. Administering NaFeEDTA orally elevated urinary Cu, Fe, and Zn excretion compared with FeSO 4 (1.41-, 11.9-, and 13.9-fold higher, respectively). We conclude that iron is dissociated from the EDTA complex prior to or during intestinal absorption. A portion of intact FeEDTA may be absorbed via a paracellular route at high levels of intake but is mostly excreted in the urine. Metal-free EDTA may be absorbed and cause elevated urinary excretion of Fe, Cu, and Zn.

Altered dietary iron intake is a strong modulator of renal DMT1 expression

Divalent metal transporter1 (DMT1; also known as DCT1 or NRAMP2) is an important component of the cellular machinery responsible for dietary iron absorption in the duodenum. DMT1 is also highly expressed in the kidney where it has been suggested to play a role in urinary iron handling. In this study, we determined the effect on renal DMT1 expression of feeding an iron-restricted diet (50 mg/kg) or an iron-enriched diet (5 g/kg) for 4 wk and measured urinary and fecal iron excretion rates. Feeding the low-iron diet caused a reduction in serum iron concentration and fecal iron output rate with an increase in renal DMT1 expression. Feeding an iron-enriched diet had the converse effect. Therefore, DMT1 expression in the kidney is sensitive to dietary iron intake, and the level of expression is inversely related to the dietary iron content. Changes in DMT1 expression occurred intracellularly in the proximal tubule and in the apical membrane and subapical region of the distal convoluted tubule. Increased DMT1 expression was accompanied by a decrease in urinary iron excretion rate and vice versa when DMT1 expression was reduced. Together, these findings suggest that modulation of renal DMT1 expression may influence renal iron excretion rate.

Iron status in Danish women, 1984-1994: a cohort comparison of changes in iron stores and the prevalence of iron deficiency and iron overload

BACKGROUND AND OBJECTIVES

From 1954 to 1986, flour in Denmark was fortified with 30 mg carbonyl iron per kilogram. This mandatory enrichment of cereal products was abolished in 1987. The aim was to evaluate iron status in the Danish female population before and after abolishment of iron fortification.

METHODS

Iron status, serum ferritin and haemoglobin, was assessed in population surveys in 1983-1984 comprising 1221 Caucasian women (1089 non-blood-donors, 130 donors) and in 1993-1994 comprising 1261 women (1155 non-blood-donors, 104 donors) equally distributed in age cohorts of 40, 50, 60 and 70 yr.

RESULTS

In the 1984 survey, median ferritin values in the four age cohorts in non-blood-donors were 44, 57, 84 and 80 microg/L, and in the 1994 survey 40, 67, 97 and 95 microg/L, respectively. In 1984, premenopausal women had median ferritin of 43 microg/L and in 1994 of 39 microg/L (NS). In 1984, postmenopausal women had median ferritin of 75 microg/L and in 1994 of 93 microg/L (P < 0.0001). The prevalence of depleted iron stores (ferritin < 16 microg/L) was not significantly different in 1984 and 1994 either in premenopausal or in postmenopausal women. The prevalence of small + depleted iron stores (ferritin <or=32 microg/L) was not significantly different in 1984 compared with 1994 either in premenopausal women (35.8% vs. 41.0%) (P = 0.15) or in postmenopausal women (9.7% vs. 7.4%) (P = 0.15). There was no significant difference between the two surveys concerning the prevalence of iron deficiency anaemia (ferritin <13 microg/L and haemoglobin <5th percentile for iron replete women). From 1984 to 1994, the prevalence of iron overload (ferritin >300 microg/L) was unchanged in premenopausal women and had increased from 2.4% to 5.5% in postmenopausal women (P = 0.003). During the study period there was an increase in body mass index both in premenopausal and postmenopausal women (P = 0.06 and P = 0.008). Postmenopausal women displayed an increase in alcohol consumption (P < 0.0001) and a decrease in tobacco smoking (P < 0.001). In premenopausal women, there was a marked increase in the use of non-steroid anti-inflammatory drugs (P < 0.0001) in the study period, while this was unchanged in postmenopausal women. In premenopausal blood donors, median ferritin decreased from 1984 to 1994 (36 microg/L vs. 24 microg/L, P < 0.06). In postmenopausal blood donors, ferritin was not significantly different from 1984 to 1994 (50 microg/L vs. 41 microg/L, P = 0.15).

CONCLUSION

Abolition of iron fortification reduced the median dietary iron intake in Danish women from 12 to 9 mg/d. Despite the absence of food iron fortification, from 1984 to 1994, body iron stores were unchanged in premenopausal women, whereas iron stores and the prevalence of iron overload in postmenopausal women had increased significantly. The reason appears to be the changes in dietary habits with a lower consumption of dairy products and eggs, which inhibit iron absorption, and a higher consumption of alcohol, meat and poultry, containing heme iron and enhancing iron absorption.

Iron status in Danish men 1984-94: a cohort comparison of changes in iron stores and the prevalence of iron deficiency and iron overload

BACKGROUND AND OBJECTIVES

From 1954 to 1987, flour in Denmark was fortified with 30 mg carbonyl iron per kg. This mandatory fortification was abolished in 1987. The aim of this study was to compare iron status in Danish men before and after abolition of iron fortification.

METHODS

Iron status (serum ferritin, haemoglobin), was assessed in population surveys in Copenhagen County during 1983-84 comprising 1324 Caucasian men (1024 non-blood-donors, 300 blood donors) and in 1993-94 comprising 1288 Caucasian men (1103 non-blood-donors, 185 donors), equally distributed in age cohorts of 40, 50, 60 and 70 yr.

RESULTS

In the 1984 survey median serum ferritin values in the four age cohorts in non-blood-donors were 136, 141, 133 and 111 microg/L, and in the 1994 survey 177, 173, 186 and 148 microg L(-1), respectively. The difference was significant in all age groups (P<0.001). There was no significant difference between the two surveys concerning the prevalence of small iron stores (ferritin 16-32 micro g L(-1)), depleted iron stores (ferritin <16 microg L(-1)) or iron-deficiency anaemia (ferritin <13 microg L(-1) and Hb <5th percentile for iron-replete men). However, from 1984 to 1994, the prevalence of iron overload (ferritin >300 microg L(-1)) increased from 11.3% to 18.9% (P<0.0001). During the study period there was an increase in body mass index (P<0.0001), alcohol consumption (P<0.03) and use of non-steroid anti-inflammatory drugs (NSAID) (P<0.0001), and a decrease in the use of vitamin-mineral supplements (P<0.04) and in the prevalence of tobacco smoking (P<0.0001). In contrast, median ferritin in blood donors showed a significant fall from 1984 to 1994 (103 vs. 74 micro g L(-1), P<0.02).

CONCLUSION

Abolition of iron fortification reduced the iron content of the Danish diet by an average of 0.24 mg MJ(-1), and the median dietary iron intake in men from 17 to 12 mg d(-1). From 1984 to 1994, body iron stores and the prevalence of iron overload in Danish men increased significantly, despite the abolition of food iron fortification. The reason appears to be changes in dietary habits, with a lower consumption of dairy products and eggs, which inhibit iron absorption, and a higher consumption of alcohol, meat, and poultry, containing haem iron and enhancing iron absorption. The high prevalence of iron overload in men may constitute a health risk.

Genetic differences in hepatic lipid peroxidation potential and iron levels in mice

Oxidative damage to macromolecules, including lipids, has been hypothesized as a mechanism of aging. One end product of lipid peroxidation, malondialdehyde (MDA), is often quantified as a measure of oxidative damage to lipids. We used a commercial colorimetric assay for MDA (Bioxytech LPO-586, Oxis International, Portland, OR) to measure lipid peroxidation potential in liver tissue from young (2 month) male mice from recombinant inbred (RI) mouse strains from the C57BL/6J (B6)xDBA/2J (D2) series (BXD). The LPO-586 assay (LPO) reliably detected significant differences (P<0.0001) in lipid peroxidation potential between the B6 and D2 parental strains, and yielded a more than two-fold variation across the BXD RI strains. In both B6 and D2 mice, LPO results were greater in old (23 month) mice, with a larger age-related increase in the D2 strain. As the level of iron can influence lipid peroxidation, we also measured hepatic non-heme iron levels in the same strains. Although iron level exhibited a slightly negative overall correlation (r(2)=0.119) with LPO results among the entire group of BXD RI strains, a sub-group with lower LPO values were highly correlated (r(2)=0.704). LPO results were also positively correlated with iron levels from a group of 8 other inbred mouse strains (r(2)=0.563). The BXD RI LPO data were statistically analyzed to nominate quantitaive trait loci (QTL). A single marker, Zfp4, which maps to 55.2 cM on chromosome 8, achieved a significance level of P<0.0006. At least two potentially relevant candidate genes reside close to this chromosomal position. Hepatic lipid peroxidation potential appears to be a strain related trait in mice that is amenable to QTL analysis.