Hepcidin, an antimicrobial peptide is downregulated in ceruloplasmin-deficient mice

Association between iron metabolism and non-alcoholic fatty liver disease: results from the National Health and Nutrition Examination Survey (NHANES 2017-2018) and a controlled animal study

BACKGROUND

Iron metabolism may be involved in the pathogenesis of the non-alcoholic fatty liver disease (NAFLD). The relationship between iron metabolism and NAFLD has not been clearly established. This study aimed to clarify the relationship between biomarkers of iron metabolism and NAFLD.

METHODS

Based on the National Health and Nutrition Examination Survey (NHANES), restricted cubic spline models and multivariable logistic regression were used to examine the association between iron metabolism [serum iron (SI), serum ferritin (SF), transferrin saturation (TSAT), and soluble transferrin receptor (sTfR)] and the risk for NAFLD. In addition, stratified subgroup analysis was performed for the association between TSAT and NAFLD. Moreover, serum TSAT levels were determined in male mice with NAFLD. The expression of hepcidin and ferroportin, vital regulators of iron metabolism, were analyzed in the livers of mice by quantitative real-time PCR (qRT-PCR) and patients with NAFLD by microarray collected from the GEO data repository.

RESULTS

Patients with NAFLD showed decreased SI, SF, and TSAT levels and increased STfR levels based on the NHANES. After adjusting for confounding factors, TSAT was significantly negatively correlated with NAFLD. Of note, the relationship between TSAT and NAFLD differed in the four subgroups of age, sex, race, and BMI (P for interaction < 0.05). Consistently, mice with NAFLD exhibited decreased serum TSAT levels. Decreased hepcidin and increased ferroportin gene expression were observed in the livers of patients and mice with NAFLD.

CONCLUSION

Serum TSAT levels and hepatic hepcidin expression were decreased in both patients and mice with NAFLD. Among multiple biomarkers of iron metabolism, lower TSAT levels were significantly associated with a higher risk of NAFLD in the U.S. general population. These findings might provide new ideas for the prediction, diagnosis, and mechanistic exploration of NAFLD.

[Aceruloplasminemia, a rare condition not to be overlooked]

Aceruloplasminemia is a rare iron-overload disease that should be better known by physicians. It is an autosomal recessive disorder due to mutations in ceruloplasmin gene causing systemic iron overload, including cerebral and liver parenchyma. The impairment of ferroxidase ceruloplasmin activity leads to intracellular iron retention leading aceruloplasminemia symptoms. Neurologic manifestations include cognitive impairment, ataxia, extrapyramidal syndrome, abnormal movements, and psychiatric-like syndromes. Physicians should search for aceruloplasminemia in several situations with high ferritin levels: microcytic anaemia, diabetes mellitus, neurological and psychiatric disorders. Diagnosis approach is based on the study of transferrin saturation and hepatic iron content evaluated by magnetic resonance imaging of the liver. Ceruloplasmin dosage is required in case of low transferrin saturation and high hepatic iron content and genetic testing is mandatory in case of serum ceruloplasmin defect. Neurological manifestations occur in the sixties decade and leads to disability. Iron chelators are widely used. Despite their efficacy on systemic and cerebral iron overload, iron chelators tolerance is poor. Early initiation of iron chelation therapy might prevent or slowdown neurodegeneration, highlighting the need for an early diagnosis but their clinical efficacy remains uncertain.

Functional iron deficiency in toxic milk mutant mice (tx-J) despite high hepatic ferroportin: a critical role of decreased GPI-ceruloplasmin expression in liver macrophages

Jackson toxic milk mutant mice (tx-J) carrying a missense mutation in the Atp7b gene are animal models of the Wilson disease. In both the Wilson patients and the tx-J mice, mutations in the ATP7B/Atp7b gene lead to disturbances in copper metabolism. The dysfunction of ATP7B/Atp7b leads to a reduction in the incorporation of copper into apoceruloplasmin; this decreases the ferroxidase activity of ceruloplasmin necessary for the efflux of iron from cells and reduces the release of copper from hepatocytes to the bile; this results in a massive hepatic copper accumulation. A decrease in the ferroxidase activity of ceruloplasmin in the tx-J mice emphasises the practicality of this animal model for the exploration of disturbances in iron balance triggered by dysregulation of copper metabolism. We found that 6-month-old tx-J mutants developed mild anaemia caused by functional iron deficiency. The tx-J mutants showed decreased plasma iron levels with concomitant iron accumulation in hepatocytes and liver macrophages. Hepatic iron retention was accompanied by decreased expression of the membrane form of ceruloplasmin in both liver cell types. Interestingly, in the liver of mutants, we found high levels of ferroportin (an iron exporter) on the surface of liver macrophages despite increased hepatic expression of hepcidin, a peptide inducing internalization and degradation of ferroportin. We conclude that even when the ferroportin expression is high, ceruloplasmin remains a limiting factor in the release of iron to the extracellular environment.

Aceruloplasminemia: A Severe Neurodegenerative Disorder Deserving an Early Diagnosis

Aceruloplasminemia (ACP) is a rare, adult-onset, autosomal recessive disorder, characterized by systemic iron overload due to mutations in the Ceruloplasmin gene (CP), which in turn lead to absence or strong reduction of CP activity. CP is a ferroxidase that plays a key role in iron export from various cells, especially in the brain, where it maintains the appropriate iron homeostasis with neuroprotective effects. Brain iron accumulation makes ACP unique among systemic iron overload syndromes, e.g., various types of genetic hemochromatosis. The main clinical features of fully expressed ACP include diabetes, retinopathy, liver disease, and progressive neurological symptoms reflecting iron deposition in target organs. However, biochemical signs of the disease, namely a mild anemia mimicking iron deficiency anemia because of microcytosis and low transferrin saturation, but with "paradoxical" hyperferritinemia, usually precedes the onset of clinical symptoms of many years and sometimes decades. Prompt diagnosis and therapy are crucial to prevent neurological complications of the disease, as they are usually irreversible once established. In this mini-review we discuss some major issues about this rare disorder, pointing out the early clues to the right diagnosis, instrumental to reduce significant disability burden of affected patients.

Iron Pathophysiology in Stroke

Ischemic and hemorrhagic stroke are the common types of stroke that lead to brain injury neurological deficits and mortality. All forms of stroke remain a serious health issue, and there is little successful development of drugs for treating stroke. Incomplete understanding of stroke pathophysiology is considered the main barrier that limits this research progress. Besides mitochondria and free radical-producing enzymes, labile iron is an important contributor to oxidative stress. Although iron regulation and metabolism in cerebral stroke are not fully understood, much progress has been achieved in recent years. For example, hepcidin has recently been recognized as the principal regulator of systemic iron homeostasis and a bridge between inflammation and iron regulation. This review discusses recent research progress in iron pathophysiology following cerebral stroke, focusing molecular regulation of iron metabolism and potential treatment targets.

Phenotypic heterogeneity in seven Italian cases of aceruloplasminemia

INTRODUCTION

Aceruloplasminemia is an ultra-rare hereditary disorder characterized by iron-restricted microcytic anemia and tissue iron overload associated with diabetes, retinal and progressive neurological degeneration. We describe genotypes and phenotypes at diagnosis, and disease evolution of seven Italian patients.

METHODS

Anagraphical, biochemical, genetic, clinical and instrumental data were collected at diagnosis and during a long-term follow-up. Mutations, ferroxidase activity and Western Blot analysis of ceruloplasmin were performed according to standard protocols.

RESULTS

Three mutations were already described (p.Phe217Ser, deletions of exon 11 and 12), p.Ile991Thr is a very rare variant, p.Cys338Ser and IVS6+1G > A were novel mutations. In silico analyses suggested they were highly likely or likely to be damaging. At diagnosis, 100% had microcytosis, 86% had mild-moderate anemia, low serum iron and high serum ferritin. Four (57%) had type 1 diabetes or glucose intolerance, 3/7 had neurological manifestations, and only one had early diabetic retinopathy. All but one underwent iron chelation therapy requiring temporary discontinuation because of anemia worsening. At the end of follow-up, three patients aggravated and 2 developed neurological symptoms; only two patients were free of neurological manifestations and showed mild or absent brain iron.

CONCLUSION

Aceruloplasminemia phenotypes ranged from classical characterized by progressive neurologic derangement to milder in which signs of systemic iron overload prevailed over brain iron accumulation. Within this large heterogeneity, microcytosis with or without anemia, low serum iron and high serum ferritin were the early hallmarks of the disease. Therapeutic approaches other than iron chelation should be explored to reduce morbidity and improve life expectancy.

Iron metabolism and related genetic diseases: A cleared land, keeping mysteries

Body iron has a very close relationship with the liver. Physiologically, the liver synthesizes transferrin, in charge of blood iron transport; ceruloplasmin, acting through its ferroxidase activity; and hepcidin, the master regulator of systemic iron. It also stores iron inside ferritin and serves as an iron reservoir, both protecting the cell from free iron toxicity and ensuring iron delivery to the body whenever needed. The liver is first in line for receiving iron from the gut and the spleen, and is, therefore, highly exposed to iron overload when plasma iron is in excess, especially through its high affinity for plasma non-transferrin bound iron. The liver is strongly involved when iron excess is related either to hepcidin deficiency, as in HFE, hemojuvelin, hepcidin, and transferrin receptor 2 related haemochromatosis, or to hepcidin resistance, as in type B ferroportin disease. It is less involved in the usual (type A) form of ferroportin disease which targets primarily the macrophagic system. Hereditary aceruloplasminemia raises important pathophysiological issues in light of its peculiar organ iron distribution.

Sex differences in iron status and hepcidin expression in rats

Studies have shown that men and women exhibit significant differences regarding iron status. However, the effects of sex on iron accumulation and distribution are not well established. In this study, female and male Sprague-Dawley rats were killed at 4 months of age. Blood samples were analyzed to determine the red blood cell (RBC) count, hemoglobin (Hb) concentration, hematocrit (Hct), and mean red blood cell volume (MCV). The serum samples were analyzed to determine the concentrations of serum iron (SI), transferrin saturation (TS), ferritin, soluble transferrin receptor (sTfR), and erythropoietin (EPO). The tissue nonheme iron concentrations were measured in the liver, spleen, bone marrow, kidney, heart, gastrocnemius, duodenal epithelium, lung, pallium, cerebellum, hippocampus, and striatum. Hepatic hepcidin expression was detected by real-time PCR analysis. The synthesis of ferroportin 1 (FPN1) in the liver, spleen, kidney, and bone marrow was determined by Western blot analysis. The synthesis of duodenal cytochrome B561 (DcytB), divalent metal transporter 1 (DMT1), FPN1, hephaestin (HP) in the duodenal epithelium was also measured by Western blot analysis. The results showed that the RBC, Hb, and Hct in male rats were higher than those in female rats. The SI and plasma TS levels were lower in male rats than in female rats. The levels of serum ferritin and sTfR were higher in male rats than in female rats. The EPO levels in male rats were lower than that in female rats. The nonheme iron contents in the liver, spleen, bone marrow, and kidney in male rats were also lower (56.7, 73.2, 60.6, and 61.4 % of female rats, respectively). Nonheme iron concentrations in the heart, gastrocnemius, duodenal epithelium, lung, and brain were similar in rats of both sexes. A moderate decrease in hepatic hepcidin mRNA content was also observed in male rats (to 56.0 % of female rats). The levels of FPN1 protein in the liver, spleen, and kidney were higher in male rats than in female rats. There was no significant change in FPN1 expression in bone marrow. Significant difference was also not found in DcytB, DMT1, FPN1, and HP protein levels in the duodenal epithelium between male and female rats. These data suggest that iron is distributed differently in male and female rats. This difference in iron distribution may be associated with the difference in the hepcidin level.

The regulation of iron metabolism in the mononuclear phagocyte system

The daily iron absorption and loss are small and iron metabolism in human is characterized by a limited external exchange and by an efficient reutilization of iron from internal sources. The mononuclear phagocyte system (MPS) plays a key role in recycling iron from hemoglobin of senescent or damaged erythrocytes, which is important in maintaining iron homeostasis. Many iron-related proteins are expressed in the MPS, including heme oxygenase (HO) for heme degradation, the iron importer transferrin receptor 1 (TfR1) and divalent metal transport 1 (DMT1), the iron exporter ferroportin 1 (FPN1) and the iron regulatory hormone hepcidin. Insights into the regulatory mechanisms that control the regulation of iron metabolism proteins in the MPS will deepen our understanding about the molecular mechanism of iron homeostasis and iron-related diseases.

Aceruloplasminemia: an update

Aceruloplasminemia is an inherited neurodegenerative disorder involving "neurodegeneration with brain iron accumulation," which is caused by genetic defects in the ceruloplasmin gene. Ceruloplasmin is a multicopper oxidase with ferroxidase activity that oxidizes ferrous iron following its transfer to extracellular transferrin. In the central nervous system, a glycosylphosphatidylinositol-linked ceruloplasmin bound to the cell membranes was found to be the major isoform of this protein. Aceruloplasminemia is characterized by diabetes, retinal degeneration, and progressive neurological symptoms, including extrapyramidal symptoms, ataxia, and dementia. Clinical and pathological studies and investigations of cell culture and murine models revealed that there is an iron-mediated cellular radical injury caused by a marked accumulation of iron in the affected parenchymal tissues. The aim of this chapter is to provide an overview of not only the clinical features, genetic and molecular pathogenesis, and treatment of aceruloplasminemia but also the biological and physiological features of iron metabolism.

Measurement of serum hepcidin-25 levels as a potential test for diagnosing hemochromatosis and related disorders

BACKGROUND

Iron overload syndromes include a wide spectrum of genetic and acquired conditions. Recent studies suggest suppressed hepcidin synthesis in the liver to be the molecular basis of hemochromatosis. However, a liver with acquired iron overload synthesizes an adequate amount of hepcidin. Thus, hepcidin could function as a biochemical marker for differential diagnosis of iron overload syndromes.

METHODS

We measured serum iron parameters and hepcidin-25 levels followed by sequencing HFE, HJV, HAMP, TFR2, and SLC40A1 genes in 13 Japanese patients with iron overload syndromes. In addition, we performed direct measurement of serum hepcidin-25 levels using liquid chromatography-tandem mass spectrometry in 3 Japanese patients with aceruloplasminemia and 4 Italians with HFE hemochromatosis.

RESULTS

One patient with HJV hemochromatosis, 2 with TFR2 hemochromatosis, and 3 with ferroportin disease were found among the 13 Japanese patients. The remaining 7 Japanese patients showed no evidence for genetic basis of iron overload syndrome. As far as the serum hepcidin-25 was concerned, seven patients with hemochromatosis and 3 with aceruloplasminemia showed markedly decreased serum hepcidin-25 levels. In contrast, 3 patients with ferroportin disease and 7 with secondary iron overload syndromes showed serum hepcidin levels parallel to their hyperferritinemia. Patients with iron overload syndromes were divided into 2 phenotypes presenting as low and high hepcidinemia. These were then associated with their genotypes.

CONCLUSION

Determining serum hepcidin-25 levels may aid differential diagnosis of iron overload syndromes prior to genetic analysis.

Evidence for a critical role of ceruloplasmin oxidase activity in iron metabolism of Wilson disease gene knockout mice

BACKGROUND AND AIM

Wilson disease is a genetic disorder associated with copper overload due to mutations within the ATP7B gene. Although copper and iron metabolism are closely linked, the influence of mutations of the ATP7B gene on iron homeostasis is unknown. Therefore, the present study was carried out to elucidate iron metabolism in Atp7b(-/-) mice, an animal model of Wilson disease.

METHODS

Hepatic iron content, serum iron parameters and blood hemoglobin levels of Atp7b(-/-) mice and wild type mice were studied. Hepatic and duodenal expression of iron metabolism-related genes was measured quantitatively by real-time reverse transcription-polymerase chain reaction and post-translational expression of Dmt1 was analyzed by immunoblot.

RESULTS

Atp7b(-/-) mice displayed copper accumulation (P < 0.001), slightly elevated hepatic iron content (P = NS), and a low serum ceruloplasmin oxidase activity (1.5 +/- 1.9 U/L vs 18.9 +/- 4.0 U/L, P < 0.001) when compared with wild type mice. Serum iron, serum transferrin saturation, and blood hemoglobin levels were significantly lower in Atp7b(-/-) mice compared with controls (121.2 +/- 35.3 microg/dL vs 201.8 +/- 34.9 microg/dL (P < 0.001); 44.0 +/- 12.7% vs 68.0 +/- 8.2% (P < 0.001); and 12.7 +/- 0.2 g/dl vs 15.3 +/- 0.1 g/dl (P < 0.001), respectively). Hepatic mRNA expression of hepcidin, TfR-1, TfR-2, hemojuvelin, and Dmt1 + IRE did not differ significantly between Atp7b(-/-) and wild type mice. In the duodenum of Atp7b(-/-) mice Dmt1 + IRE and hephaestin did not show any differences in their mRNA levels compared with wild type mice, while Dcytb mRNA expression was 1.7-fold increased compared with wild type mice (P = 0.01).

CONCLUSION

Atp7b(-/-) mice demonstrated decreased serum iron parameters and hemoglobin levels most likely related to a low serum ceruloplasmin oxidase activity and not due to total body iron deficiency.