Transferrin receptor distribution and iron deposition in the hepatic lobule of iron-overloaded rats

Dietary Iron Overload Differentially Modulates Chemically-Induced Liver Injury in Rats

Hepatic iron overload is well known as an important risk factor for progression of liver diseases; however, it is unknown whether it can alter the susceptibility to drug-induced hepatotoxicity. Here we investigate the pathological roles of iron overload in two single-dose models of chemically-induced liver injury. Rats were fed a high-iron (Fe) or standard diet (Cont) for four weeks and were then administered with allyl alcohol (AA) or carbon tetrachloride (CCl₄). Twenty-four hours after administration mild mononuclear cell infiltration was seen in the periportal/portal area (Zone 1) in Cont-AA group, whereas extensive hepatocellular necrosis was seen in Fe-AA group. Centrilobular (Zone 3) hepatocellular necrosis was prominent in Cont-CCl₄ group, which was attenuated in Fe-CCl₄ group. Hepatic lipid peroxidation and hepatocellular DNA damage increased in Fe-AA group compared with Cont-AA group. Hepatic caspase-3 cleavage increased in Cont-CCl₄ group, which was suppressed in Fe-CCl₄ group. Our results showed that dietary iron overload exacerbates AA-induced Zone-1 liver injury via enhanced oxidative stress while it attenuates CCl₄-induced Zone-3 liver injury, partly via the suppression of apoptosis pathway. This study suggested that susceptibility to drugs or chemical compounds can be differentially altered in iron-overloaded livers.

Involvement of cytosolic and mitochondrial iron in iron overload cardiomyopathy: an update

Iron overload cardiomyopathy (IOC) is a major cause of death in patients with diseases associated with chronic anemia such as thalassemia or sickle cell disease after chronic blood transfusions. Associated with iron overload conditions, there is excess free iron that enters cardiomyocytes through both L- and T-type calcium channels thereby resulting in increased reactive oxygen species being generated via Haber-Weiss and Fenton reactions. It is thought that an increase in reactive oxygen species contributes to high morbidity and mortality rates. Recent studies have, however, suggested that it is iron overload in mitochondria that contributes to cellular oxidative stress, mitochondrial damage, cardiac arrhythmias, as well as the development of cardiomyopathy. Iron chelators, antioxidants, and/or calcium channel blockers have been demonstrated to prevent and ameliorate cardiac dysfunction in animal models as well as in patients suffering from cardiac iron overload. Hence, either a mono-therapy or combination therapies with any of the aforementioned agents may serve as a novel treatment in iron-overload patients in the near future. In the present article, we review the mechanisms of cytosolic and/or mitochondrial iron load in the heart which may contribute synergistically or independently to the development of iron-associated cardiomyopathy. We also review available as well as potential future novel treatments.

Duodenal absorption and tissue utilization of dietary heme and nonheme iron differ in rats

BACKGROUND

Dietary heme contributes to iron intake, yet regulation of heme absorption and tissue utilization of absorbed heme remains undefined.

OBJECTIVES

In a rat model of iron overload, we used stable iron isotopes to examine heme- and nonheme-iron absorption in relation to liver hepcidin and to compare relative utilization of absorbed heme and nonheme iron by erythroid (RBC) and iron storage tissues (liver and spleen).

METHODS

Twelve male Sprague-Dawley rats were randomly assigned to groups for injections of either saline or iron dextran (16 or 48 mg Fe over 2 wk). After iron loading, rats were administered oral stable iron in the forms of (57)Fe-ferrous sulfate and (58)Fe-labeled hemoglobin. Expression of liver hepcidin and duodenal iron transporters and tissue stable iron enrichment was determined 10 d postdosing.

RESULTS

High iron loading increased hepatic hepcidin by 3-fold and reduced duodenal expression of divalent metal transporter 1 (DMT1) by 76%. Nonheme-iron absorption was 2.5 times higher than heme-iron absorption (P = 0.0008). Absorption of both forms of iron was inversely correlated with hepatic hepcidin expression (heme-iron absorption: r = -0.77, P = 0.003; nonheme-iron absorption: r = -0.80, P = 0.002), but hepcidin had a stronger impact on nonheme-iron absorption (P = 0.04). Significantly more (57)Fe was recovered in RBCs (P = 0.02), and more (58)Fe was recovered in the spleen (P = 0.01).

CONCLUSIONS

Elevated hepcidin significantly decreased heme- and nonheme-iron absorption but had a greater impact on nonheme-iron absorption. Differential tissue utilization of heme vs. nonheme iron was evident between erythroid and iron storage tissues, suggesting that some heme may be exported into the circulation in a form different from that of nonheme iron.

In situ detection of TGF betas, TGF beta receptor II mRNA and telomerase activity in rat cholangiocarcinogenesis

AIM: Initial report on the in situ examination of the mRNA expression of transforming growth factor betas (TGFβs), TGFβ type II receptor (TβRII) and telomerase activity in the experimental rat liver tissue during cholangiocarcinogenesis.

METHODS: Rat liver cholangiocarcinogenesis was induced by 3’-methyl 4-dimethylazobenzene (3’Me-DAB). In situ hybridization was used to examine the TGFβs) and TGFβ type II receptor (TβRII) mRNA, in situ TRAP was used to check the telomerase activity in the tissue samples.

RESULTS: There was no TGFβs, TβRII mRNA expression or telomerase activity in the control rat cholangiocytes. The expression of TGFβ1, TβRII was increased in regenerative, hyperplastic, dysplastic cholangiocytes and cholangiocarcinoma (CC) cells. The expression of TGFβ2 mRNA was observed in only a part of hyperplastic, dysplastic cholangiocytes. TGFβ3 expression was very weak, only in hyperplastic lesion. There was positive telomerase activity in the regenerative, hyperplastic, dysplastic cholangiocytes, and CC cells. Stroma fibroblasts of these lesions also showed positive TGFβs, TβRII mRNA expression and telomerase activity.

CONCLUSION: There were TGFβs, TβRII expression and telomerase activity in hyperplastic, dysplastic cholangiocytes, cholangiocarcinoma cells as well as in stroma fibroblasts during cholangiocarcinogenesis. Their expression or activity is important in cholangiocarcinogenesis andstroma formation.

Coincident increase in periportal expression of iron proteins in the iron-loaded rat liver

BACKGROUND

The liver is the major iron storage organ in the body and, as a result, total body iron stores closely regulate hepatocyte iron uptake, storage and release. Transferrin, transferrin receptor and ferritin facilitate these processes.

METHODS

Expression of the three proteins was localized by immunohistochemistry and in situ hybridization on normal, iron-loaded and iron-deficient rat livers. Gel shift assays were used to determine iron regulatory protein (IRP) binding activity.

RESULTS

In the normal rat liver, all three proteins and mRNA were evenly distributed throughout the hepatic lobule. In iron-loaded liver, increased iron stores were found in a periportal distribution, coinciding with increased periportal protein levels of each protein. Periportal transferrin and ferritin mRNA levels were also increased. Hepatic transferrin and transferrin receptor expression was increased in iron deficiency compared with controls; however, despite no change in ferritin mRNA levels being found, ferritin protein was not detected. Hepatic IRP2 binding activity was decreased in iron loading and increased in iron deficiency.

CONCLUSION

The combined findings of this study were that, in the dietary iron-loaded rat model, increased iron stores were localized to periportal hepatocytes and that these same hepatocytes also had increased ferritin, transferrin receptor and transferrin protein expression. This response suggests that additional, non-IRP control mechanisms may be involved in the regulation or stability of these proteins. In iron deficiency the inverse post-transcriptional regulation of ferritin and transferrin receptor was consistent with IRP regulation.