Hepatic transferrin plays a role in systemic iron homeostasis and liver ferroptosis

Although the serum-abundant metal-binding protein transferrin (encoded by the Trf gene) is synthesized primarily in the liver, its function in the liver is largely unknown. Here, we generated hepatocyte-specific Trf knockout mice (Trf-LKO), which are viable and fertile but have impaired erythropoiesis and altered iron metabolism. Moreover, feeding Trf-LKO mice a high-iron diet increased their susceptibility to developing ferroptosis-induced liver fibrosis. Importantly, we found that treating Trf-LKO mice with the ferroptosis inhibitor ferrostatin-1 potently rescued liver fibrosis induced by either high dietary iron or carbon tetrachloride (CCl4) injections. In addition, deleting hepatic Slc39a14 expression in Trf-LKO mice significantly reduced hepatic iron accumulation, thereby reducing ferroptosis-mediated liver fibrosis induced by either a high-iron diet or CCl4 injections. Finally, we found that patients with liver cirrhosis have significantly lower levels of serum transferrin and hepatic transferrin, as well as higher levels of hepatic iron and lipid peroxidation, compared with healthy control subjects. Taken together, these data indicate that hepatic transferrin plays a protective role in maintaining liver function, providing a possible therapeutic target for preventing ferroptosis-induced liver fibrosis.

The role of nerve inflammation and exogenous iron load in experimental peripheral diabetic neuropathy (PDN)

BACKGROUND

Iron is an essential but potentially toxic metal in mammals. Here we investigated a pathogenic role of exogenous iron in peripheral diabetic neuropathy (PDN) in an animal model for type 1 diabetes.

METHODS

Diabetes was induced by a single injection of streptozotocin (STZ) in 4-month-old Sprague-Dawley rats. STZ-diabetic rats and non-diabetic rats were fed with high, standard, or low iron diet. After three months of feeding, animals were tested.

RESULTS

STZ-rats on standard iron diet showed overt diabetes, slowed motor nerve conduction, marked degeneration of distal intraepidermal nerve fibers, mild intraneural infiltration with macrophages and T-cells in the sciatic nerve, and increased iron levels in serum and dorsal root ganglion (DRG) neurons. While motor fibers were afflicted in all STZ-groups, only a low iron-diet led also to reduced sensory conduction velocities in the sciatic nerve. In addition, only STZ-rats on a low iron diet showed damaged mitochondria in numerous DRG neurons, a more profound intraepidermal nerve fiber degeneration indicating small fiber neuropathy, and even more inflammatory cells in sciatic nerves than seen in any other experimental group.

CONCLUSIONS

These results indicate that dietary iron-deficiency rather than iron overload, and mild inflammation may both promote neuropathy in STZ-induced experimental PDN.

Blood mononucleocytes are sensitive to the DNA damaging effects of iron overload--in vitro and ex vivo results with human and rat cells

Iron exposure enhances colorectal carcinogeneis, by producing reactive oxygen species, which damage lipids, proteins and DNA. We recently demonstrated that ferric-nitrilotriacetate (Fe-NTA) damages DNA of human colon cells in different stages of malignant transformation. Opposed to this, little is known on systemic effects of iron and it is still difficult to determine the border between essential iron supplementation and iron overload in humans. The aim of this study was to determine whether Fe-NTA causes global and specific DNA damage in peripheral leucocytes. Human leucocytes were treated in vitro with Fe-NTA for 30 min at 37 degrees C. Male Sprague Dawley rats were fed (6 weeks) with an iron-overload diet (9.9 g Fe/kg DM) and whole blood was collected. DNA damage was measured in human and rat blood cells using the alkaline version of the Comet Assay with repair specific enzymes. In human cells the distribution of TP53 in the comet images was detected using fluorescence in situ hybridization (Comet FISH) to measure DNA damage in the region of the TP53 gene. Fe-NTA (10-500 microM) was clearly genotoxic in human leucocytes in vitro, and also in leucocytes of rats fed the iron overload diet. The induced damage in human leucocytes was approximately two-fold that observed previously in human colon cells. Oxidized bases were induced by iron in rat leucocytes in vivo, while they were not induced in human leucocytes in vitro. Fe-NTA enhanced the migration of TP53 signals into the comet tail of human leucocytes, indicating a high susceptibility of this tumour-relevant gene towards DNA damage induced by iron overload. In conclusion, iron markedly induced DNA damage in human and rat leucocytes, which shows that these white blood cells are sufficiently sensitive to assess exposure to iron. The measurement of DNA damage in human leucocytes could be used as a sensitive biomarker to study iron overload in vivo in humans and thus to determine whether supplementation results in genotoxic risk.

Ascorbic acid does not increase the oxidative stress induced by dietary iron in C3H mice

Iron is a potent prooxidant that can induce lipid peroxidation. Ascorbic acid, a potent antioxidant, has prooxidant effects in the presence of iron in vitro. We investigated whether ascorbic acid and iron co-supplementation in ascorbic acid-sufficient mice increases hepatic oxidative stress. C3H/He mice were fed diets supplemented with iron to 100 mg/kg diet or 300 mg/kg diet with or without ascorbic acid (15 g/kg diet) for 3 wk. Liver iron concentration, malondialdehyde (MDA), glutathione (GSH), glutathione S-transferase (GST), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) were measured. High dietary iron increased liver iron concentrations slightly (P < 0.05), whereas it dramatically increased hepatic MDA (P < 0.0001). Ascorbic acid increased MDA but only in mice fed the low-iron diet (P < 0.05). The high-iron diet reduced GPx (P < 0.0001), CAT (P < 0.0005), SOD (P < 0.05), and GST (P < 0.005) activities regardless of ascorbic acid supplementation. In contrast, ascorbic acid reduced GPx (P < 0.0001) and CAT (P < 0.05) activities only in mice fed the low-iron diet. In conclusion, ascorbic acid supplementation can have prooxidant effects in the liver. However, ascorbic acid does not further increase the oxidative stress induced by increased dietary iron.

Does nitric oxide contribute to iron-dependent brain injury after experimental cerebral ischaemia?

Experimental and clinical data suggest that iron has a key role in cerebral ischaemia. We measure infarct volume and analyse the nitric oxide responses to brain injury in rat stroke model after increased oral iron intake. Permanent middle cerebral artery occlusion (MCAO) was performed in a group of 20 male Wistar rats, 10 of which were fed with a control diet and 10 of which were fed with iron-enriched diet containing 2.5% carbonyl iron for 9 weeks. L-arginine and nitric oxide metabolites were determined in blood samples before and at 2, 6, 8 and 48 h after MCAO. Infarct volume, thiobarbituric acid reaction substances (TBARS) and tissue iron were measured at 48 h. Infarct volume was 66% greater in the iron-fed rats than in the control group. Iron-fed animals showed significantly higher levels of TBARS. Liver iron stores (3500 +/- 199 vs 352 +/- 28 microg Fe/g, p<0.0001) but not brain iron stores (131 +/- 11 vs 139 +/- 8 microg Fe/g, p=0.617), were significantly higher in the iron-fed group. L-arginine levels were slightly lower in iron-fed rats and decreased significantly in both groups at 6 and 8 hours after MCAO. The levels of the stable end products of NOS (NOx = nitrite + nitrate) were significantly higher in iron-fed rats before MCAO (16.2 +/- 2.2 vs. 9.6 +/- 0.8 micromol x L(-1), p<0.05), with a further increase during the six first hours after MCAO in both groups. These results suggest that the iron overload that increases both superoxide and nitric oxide production leads to peroxynitrite formation, thus enhancing brain damage.

Effect of iron overload and dietary fat on indices of oxidative stress and hepatic fibrogenesis in rats

BACKGROUND/AIMS

Oxidative stress is presumed to play an important role in hepatic fibrogenesis. Diets high in polyunsaturated fatty acids (PUFA) enhance fibrosis and have been associated with increased oxidative damage in some models of liver injury. The aim of this study was to determine the effects of dietary fat of varying PUFA content on iron-induced oxidative stress and fibrosis.

METHODS

Rats were given parenteral iron and diets supplemented with coconut oil, safflower oil or menhaden oil.

RESULTS

Hepatic iron overload was associated with induction of heme oxygenase-1, a sensitive indicator of oxidative stress, and with modest increases in hydroxyproline and procollagen I mRNA levels without histologically evident fibrosis, all of which were unaffected by dietary fat. In addition, iron loading was associated with increases in cysteine, gamma-glutamylcysteine and glutathione. Dietary fat brought about the expected alterations in peroxidizability, but did not alter indices of oxidative damage.

CONCLUSION

These data highlight the distinction between oxidative stress and oxidative damage and suggest that the former is not sufficient to elicit overt fibrosis. Furthermore, while hepatic iron overload leads to oxidative stress, there is an associated upregulation of antioxidant defenses involving thiol metabolism that may be a critical factor limiting the accumulation of oxidative damage.

Iron overload enhances the development of experimental liver cirrhosis in mice

The role of iron in initiating liver fibrosis in iron overload diseases is not clearly established. Partly, this is due to the lack of suitable animal models that can produce the full liver pathology seen in genetic hemochromatosis. Recent advances in this field have demonstrated that iron may be interacting with other potential liver-damaging agents. The aim of this study was to investigate if feeding with carbonyl iron (CI) facilitates the development of carbon tetrachloride (CCl4)-induced liver fibrosis in the mouse. Mice were given a diet containing 3% CI and treated with CCl4 intraperitoneally twice weekly and 5% alcohol added to the drinking water for 12 weeks. Hepatic iron content increased 15- and 22-fold in animals receiving CI and CI + CCl4. At histological examination, iron-laden hepatocytes were found in CI treated animals, whereas these were absent in animals not exposed to CI. Mice receiving iron-enriched diet alone showed a mild fibrosis. Conversely, a marked collagen deposition was observed in CCl4 and CI + CCl4 groups. In particular, in this latter group, there was evidence of liver cirrhosis. Biochemical evaluation of collagen content substantiated histologic analysis. These results demonstrate that the addition of iron facilitates the development of cirrhosis in animals exposed to subtoxic doses of CCl4. This model may be useful in exploring the pathogenesis of liver cirrhosis. Moreover, its use in genetically altered mouse strains might provide new insight on the role of iron in fibrosis.

Iron supplementation increases disease activity and vitamin E ameliorates the effect in rats with dextran sulfate sodium-induced colitis

Inflammatory bowel disease is often associated with iron deficiency anemia and oral iron supplementation may be required. However, iron may increase oxidative stress through the Fenton reaction and thus exacerbate the disease. This study was designed to determine in rats with dextran sulfate sodium (DSS)-induced colitis whether oral iron supplementation increases intestinal inflammation and oxidative stress and whether the addition of an antioxidant, vitamin E, would reduce this detrimental effect. Four groups of rats that consumed 50 g/L DSS in drinking water were studied for 7 d and were fed: a control, nonpurified diet (iron, 270 mg, and dl-alpha-tocopherol acetate, 49 mg/kg); diet + iron (iron, 3000 mg/kg); diet + vitamin E (dl-alpha-tocopherol acetate, 2000 mg/kg) and the diet + both iron and vitamin E, each at the same concentrations as above. Body weight change, rectal bleeding, histological scores, plasma and colonic lipid peroxides (LPO), plasma 8-isoprostane, colonic glutathione peroxidase (GPx) and plasma vitamin E were measured. Iron supplementation increased disease activity as demonstrated by higher histological scores and heavier rectal bleeding. This was associated with an increase in colonic and plasma LPO and plasma 8-isoprostane as well as a decrease in colonic GPx. Vitamin E supplementation decreased colonic inflammation and rectal bleeding but did not affect oxidative stress, suggesting another mechanism for reducing inflammation. In conclusion, oral iron supplementation resulted in an increase in disease activity in this model of colitis. This detrimental effect on disease activity was reduced by vitamin E. Therefore, the addition of vitamin E to oral iron supplementation may be beneficial.

Chronic exposure to high levels of dietary iron fortification increases lipid peroxidation in the mucosa of the rat large intestine

There is increasing evidence that excess dietary iron may be a risk factor for colorectal cancer. However, the majority of animal studies looking at possible mechanism have used unrealistically high concentrations of iron. The current study was designed to test whether chronic exposure to high levels of iron fortification affects the free radical generating capacity of the lumenal contents, mucosal lipid peroxidation and crypt cell proliferation. Rats were fed diets containing either 29 mg/kg or 102 mg/kg of elemental iron for 6 mo. The free radical generating capacity of lumenal contents was assessed using an in vitro assay. Crypt cell proliferation rate was measured in tissues taken from the cecum and colon, with the remaining tissue being used for the assessment of lipid peroxidation. Chronic feeding of iron did not increase crypt cell proliferation rate in either the colon or cecum, but it was associated with an increase in free radical generating capacity in the colon and increased lipid peroxidation, particularly in the cecum. These results may be relevant to epidemiological evidence showing that dietary iron is associated with the risk of proximal colon cancer in humans.

Effect of herbo-mineral formulation EHb in experimental anaemia in rodents

EHb-a herbo-mineral formulations of iron (ferrous form) produced a significantly higher and dose dependent increase in the haemoglobin level, as compared to Fefol (a non-complex-chelated iron preparation). Also, EHb did not produce any overt toxicity or gastric irritation at these dose levels. The results suggest that EHb can be of a better choice in the treatment of anaemia than any other commercially available chelated iron preparations.

Dietary intrinsic phytate protects colon from lipid peroxidation in pigs with a moderately high dietary iron intake

High iron consumption has been proposed to relate to an increase in the risk of colon cancer, whereas high levels of supplemental sodium phytate effectively reduce iron-induced oxidative injury and reverse iron-dependent augmentation of colorectal tumorigenesis. However, the protective role of intrinsic dietary phytate has not been determined. In this study, we examined the impact of removing phytate present in a corn-soy diet by supplemental microbial phytase on susceptibility of pigs to the oxidative stress caused by a moderately high dietary iron intake. Thirty-two weanling pigs were fed the corn-soy diets containing two levels of iron (as ferrous sulfate, 80 or 750 mg/kg diet) and microbial phytase (as Natuphos, BASF, Mt. Olive, NJ, 0 or 1200 units/kg). Pigs fed the phytase-supplemented diets did not receive any inorganic phosphorus to ensure adequate degradation of phytate. After 4 months of feeding, liver, colon, and colon mucosal scrapings were collected from four pigs in each of the four dietary groups. Colonic lipid peroxidation, measured as thiobarbituric acid reacting substances (TBARS), was increased by both the high iron (P< 0.0008) and phytase (P< 0.04) supplementation. Both TBARS and F2-isoprostanes, an in vivo marker of lipid peroxidation, in colonic mucosa were affected by dietary levels of iron (P< 0.03). Mean hepatic TBARS in pigs fed the phytase-supplemented, high iron diet was 43%-65% higher than that of other groups although the differences were nonsignificant. Moderately high dietary iron induced hepatic glutathione peroxidase activity (P= 0.06) and protein expression, but decreased catalase (P< 0.05) in the colonic mucosa. In conclusion, intrinsic phytate in corn and soy was protective against lipid peroxidation in the colon associated with a moderately high level of dietary iron.

Formation of liver microsomal MDA-protein adducts in mice with chronic dietary iron overload

Lipid peroxidation has been proposed to be a major mechanism involved in the pathophysiology of hepatic iron overload. Hepatic microsomal lipid peroxidation has been demonstrated in animals with dietary iron overload, and major products of lipid peroxidation with known cytotoxicity, such as malondialdehyde (MDA), may be involved in iron-induced hepatocellular injury by covalent binding to microsomal proteins. This investigation examined whether DBA/2Ibg mice fed a diet enriched with ferrocene-iron for 16 weeks, results in hepatic lipid peroxidation, and if liver microsomes contain proteins adducted by MDA. Chronic iron feeding to mice resulted in a severe hepatic iron overload with hepatic stores of iron 12-fold greater than those measured in control mice and a three-fold increase in hepatic concentrations of MDA, indicating the occurrence of iron-induced lipid peroxidation in vivo. Hepatic collagen content was increased by over three-fold (p < 0.05) in iron-fed mice as compared to control animals, suggesting increased fibrogenesis. Using rabbit antiserum specific for MDA amine protein adducts and immunoprecipitation-Western blotting, we documented formation of 10 liver microsomal proteins adducted by MDA in iron overload mice (approximate molecular weights; 214, 140, 129, 121, 103, 83, 62, 60, 48, and 43-kD). Control mice did not exhibit positive immunostaining for these protein adducts. The incubation of synthetic MDA with liver microsomes isolated from untreated mice demonstrated formation of MDA-adducted proteins with molecular weights comparable to those detected following in vivo iron overload. The data from this animal study are the first to demonstrate that lipid-derived aldehydes produced from hepatic iron overload in vivo, covalently bind and hence, chemically modify numerous proteins in microsomes. These data suggest that MDA modified proteins in microsomes may play a role in a sequence of events that lead to cell injury during metal-induced liver damage.

Association of glutathione S-transferase isozyme-specific induction and lipid peroxidation in two inbred strains of mice subjected to chronic dietary iron overload

The alpha-class glutathione S-transferases are proposed to play a prominent role in catalyzing the conjugation of glutathione with electrophilic aldehydic products of lipid peroxidation. The effect of iron-induced lipid peroxidation on induction of glutathione S-transferase (GST) isozymes A1 and A4 in the livers of male C57/BL6Ibg and DBA/J2Ibg mice was studied. C57 and DBA mice were fed for 4 months on a diet supplemented with iron as ferrocene and then were assessed for liver injury, hepatic iron loading, indices of lipid peroxidation, GST activity, and induction of GST isozymes A1 and A4. Iron-treated animals displayed a loss in body weight from pair-fed controls and had large increases in hepatic non-heme iron with concomitant liver injury, as measured by serum alanine aminotransferase. Hepatic lipid hydroperoxides, a direct measure of oxidized membrane lipids, were significantly increased only in C57 mice, but hepatic concentrations of reduced glutathione (GSH) were significantly increased in both inbred strains. Total GST activity toward 1-chloro-2,4-dinitrobenzene was significantly increased in C57 mice but not in DBA. Western blot studies using polyclonal antibodies specific for GST A1 and A4 revealed significant increases of 1.5-2.0-fold in these GST isoforms in both inbred strains. These results in a unique murine model for hepatic iron overload further support recent in vivo studies (Khan et al., Toxicol. Appl. Pharmacol., 131, 63-72, 1995) that have associated induction of GST A4 with protection against oxidative stress-induced lipid peroxidation. The observed increases in lipid hydroperoxides, hepatic GSH, GST activity, and GST A1 and A4 protein strongly support the hypothesis that induction of GST A1 and A4 represents an important protective event in the detoxification of electrophilic products of lipid peroxidation.

Genome-linked toxic responses to dietary iron overload

Genome-related differences to Fe overload between and within rodent species were evaluated in the present study. Male B6C3F1 mice, yellow and black C5YSF1 mice, and Fischer 344 (F344) rats were fed AIN-76A diets containing 35 (control), 1,500, 3,500, 5,000, or 10,000 micrograms carbonyl Fe/g for 12 wk. No effects on body weight gain were observed in the B6C3F1 and black C5YSF1 mice, whereas at all doses of Fe above the control, weight gain was reduced in yellow C5YSF1 mice and F344 rats. At the 10,000 micrograms Fe/g dose, 9 of 12 rats died, but there was no mortality among the mice. In all animals, there was a dose-related increase in liver nonheme Fe, and the Fe was stored in hepatocytes predominantly in the periportal region. There was significant hypertrophy of the hepatocytes in both B6C3F1 mice and F344 rats fed the 10,000 micrograms Fe/g diet. PCNA assays showed significant stimulatory effects of the high dose of Fe on hepatocyte proliferation in the F344 rats and the C5YSF1 mice but not in the B6C3F1 mice. In the rat, there was pancreatic atrophy with loss of both endocrine and exocrine tissue. Morphometric evaluation of pancreas showed fewer beta cells in B6C3F1 and yellow C5YSF1 mice but not in the black C5YSF1 mice. There were fewer islets in the yellow C5YSF1 mice, and total and mean islet areas were smaller than in the control mice. Rats in the 10,000 micrograms Fe/g dose group had markedly exacerbated dose-dependent nephropathy and changes in glomerular and tubular epithelium associated with Fe accumulation. The rats also showed degeneration of the germinal epithelium of the testis, formation of multinucleated giant cells, and lack of mature sperm.

Iron overload in the rat pancreas following portacaval shunting and dietary iron supplementation

Reproduction of pancreatic iron overload in an animal model has been difficult to achieve primarily because of the first-pass extraction of iron by the liver. We hypothesized that portacaval shunting would avoid this hepatic phenomenon and increase pancreatic iron deposition. An end-to-side portacaval shunt was surgically created in male Sprague-Dawley rats, and they were subsequently fed a carbonyl iron-supplemented diet for 17 weeks. This resulted in marked iron accumulation in the pancreas (1621 +/- 188 micrograms/g) compared to minimal deposition in sham-operated rats fed the same diet (138 +/- 53 micrograms/g). Iron deposition in the acinar and centroacinar cells was confirmed histologically by Gomori staining, as well as by ultrastructural examination. Iron overloading was associated with enhanced oxidative stress evidenced by a twofold increase in the levels of glutathione disulfide and thiobarbituric acid-reactive substances. Also, adducts of proteins with malondialdehyde and 4-hydroxynonenal were demonstrated in acinar and ductal cells. Other apparent consequences of iron overload were a 50% reduction in pancreatic amylase content and a decrease in pancreatic protein concentration. These hypotrophic changes were associated with a reduced mass of zymogen granules in the acinar cells noted histologically. Our results show that a combination of portacaval shunting and carbonyl iron feeding achieve pancreatic iron overload and support the role of oxidative stress in the pathogenesis of iron-induced damage in the pancreas.