Iron Regulation and Metabolism: Abstracts from the NYC Conference Oct 2009

From the New York Academy of Science. As part of my duties here, I have chosen to remain a member of NYAS. This enables me to access many articles. These articles should add to the ongoing discussions about iron, Jak2 inhibitors, and hepcidin. The understanding of the relation between iron regulation and ineffective erythropoiesis may lead to treatments for thalassemia that will render a cure irrelevant.

Session I: Iron Regulation and Metabolism
Iron Regulation And Ineffective Erythropoiesis, Jak 2

Luca Melchiori, PhD1, Sara Gardenghi, PhD1, Ella Guy1, MD.2, Domenica Cappellini, MD3, MD1, Robert W. Grady, PhD.1, Stefano Rivella, PhD1 , 1Department of Pediatric Hematology-Oncology, Weill Medical College of Cornell University, New York, NY; 2E. Wolfson Medical Centre, Institute of Hematology, Holon, Israel, 3Centro Anemie Congenite, Fondazione Policlinico, Istituti di Ricovero e Cura a Carattere Scientifico (IRCCS), University of Milan, Milan, Italy

In thalassemia, ineffective erythropoiesis is characterized by apoptosis of the maturing nucleated erythroid cells. Our studies also suggest that limited erythroid cell differentiation plays a role in the development of ineffective erythropoiesis. Some of the major consequences of ineffective erythropoiesis are extra−medullary hematopoiesis (EMH), splenomegaly and systemic iron overload mediated by transfusion therapy and down−regulation of hepcidin. Recall that under conditions of chronic anemia, low levels of hepcidin lead to iron overload. We hypothesized that the protein kinase Jak2, which controls erythroid cell proliferation, plays a major role in exacerbating ineffective erythropoiesis. Therefore, use of Jak2 inhibitors may limit the overproduction of immature erythroid cells in thalassemia, with the potential of reversing extramedullary hematopoiesis and preventing splenectomy. For this reason, we administered a Jak2 inhibitor to mice affected by beta−thalassemia intermedia for 10 days, showing that this treatment was associated with a marked decrease in ineffective erythropoiesis, splenomegaly, no or with little or no reduction of red cell production and no side effects.

There is a clear correlation between the mass of erythroid precursors and suppression of hepcidin. Therefore, administration of a Jak2 inhibitor might also be associated with increased hepcidin synthesis and decreased iron absorption. In order to test this hypothesis we repeated the above-mentioned study in order to evaluate the level of hepcidin expression as well as that of other iron related genes. This analysis clearly indicated that the size of the spleen inversely correlated with hepcidin synthesis. In addition, blood transfusion is a pre-requisite for the management of both thalassemia−major patients and those with thalassemia−intermedia who develop splenomegaly. Therefore, administration of a Jak2 inhibitor, together with blood transfusions, might be a sensible way to further suppress ineffective erythropoiesis and limit splenomegaly/EMH. We conducted an analysis of erythropoiesis and iron metabolism in animals affected by beta−thalassemia major, which require blood transfusion for survival and compared them to transfused animals treated with placebo. Compared to latter controls, the animals treated with the Jak2 inhibitor showed a dramatic decrease in splenomegaly, amelioration of the spleen architecture and complete elimination of EMH in the liver. In addition, due to the reduction of the size of the spleen, the animals treated with the Jak2 inhibitor showed higher levels of hemoglobin at the end of the treatment, again, the spleen size inversely correlating with hepcidin synthesis. These experiments suggest that this class of compounds, if safe, might be an important tool to prevent splenectomy, reverse EMH, limit iron absorption and improve the effectiveness of transfusion therapy in patients with thalassemia.

Hepcidin in Thalassemia
Elizabeta Nemeth, PhD, David Geffen School of Medicine at UCLA, Los Angeles, CA

The iron-regulatory hormone hepcidin controls the plasma iron concentrations by blocking both the absorption of iron from the diet and the release of iron from macrophages recycling old erythrocytes. Pathological hepcidin deficiency, either relative or absolute, results in iron overload, whereas hepcidin excess causes iron restriction and anemia.

Beta thalassemia and other iron-loading anemias are characterized by inappropriately low production of hepcidin due to the strong suppressive effect of ineffective erythropoiesis. Although the precise factors are still incompletely understood, GDF15 and TWSG1 have been suggested as bone marrow-derived proteins causing hepcidin decrease. Hepcidin production is particularly low in untransfused patients, and likely accounts for the excessive iron absorption and development of the severe iron overload. In transfused patients, hepcidin levels are higher than those in untransfused, although still not appropriate for the degree of iron overload. The higher hepcidin production is due to increased iron loading and the partial relief of erythropoietic drive by transfusions. The effect of iron chelation on hepcidin production is not yet known.

The usefulness of hepcidin diagnostics or therapeutics in thalassemia syndromes remains to be demonstrated. Measurement of hepcidin levels may help stratify patients for the risk of greater iron loading or may be help assess the efficacy of therapy. Pharmacologic hepcidin agonists may help restore normal iron homeostasis in thalassemia patients, especially those not requiring transfusions. Mini-hepcidins, small peptide agonists of hepcidin, have been described which display activity in mice. The small size of these peptides may also allow oral bioavailability.

TMPRSS6: A Modifier of Hepcidin Production in Relation to Iron Stores
Matthew Heeney, Dean Campagna, Mark D. Fleming, Children's Hospital Boston, Boston, MA

The peptide hormone hepcidin is a negative regulator of iron efflux from cells. In iron deficiency anemia (IDA), hepcidin levels are ordinarily undetectable, thereby stimulating the release of iron from macrophages and duodenal enterocytes, promoting iron availability for erythropoieisis and increasing iron stores. Rare individuals with lifelong hypoferremia and microcytic anemia unresponsive to enteral and parenteral iron therapy—iron refractory iron deficiency anemia (IRIDA)—have been shown to have mutations in the hepatocyte−specific transmembrane serine protease, TMPRSS6, and that the phenotype can be attributed to excessive hepcidin production.We comprehensively analyzed hematologic and biochemical markers of iron status, inflammation, urinary and plasma hepcidin in individuals with IRIDA and their family members.

Given that the transferrin saturation (TfSat) appears to have a central role in hepcidin regulation, an index relating the hepcidin to transferrin saturation, TfSat/log10hepcidin, was evaluated to attempt to distinguish inappropriate from appropriate hepcidin expression in probands and their family members. Individuals with biallelic TMPRSS6 mutations have elevated absolute urinary and plasma hepcidin concentrations that were profoundly elevated compared to familial wild type controls when normalized for serum transferrin saturation. Furthermore, family members heterozygous for TMPRSS6 mutations had normal iron studies, but had an intermediate TfSat/log10hepcidin, indicative of a codominant phenotype. Several other individuals referred for a clinically milder IRIDA phenotype were found to have heterozygous mutations, suggesting that some heterozygotes may manifest clinically apparent disease. These data provide evidence that even heterozygous mutations in TMPRSS6 can influence systemic iron metabolism.

According to researchers at the NIH, iron overload in patients with thalassemia can be caused due to an overproduction of a protein called GDF15. This suppresses the production of a liver protein, hepcidin, which in turn leads to an increase in the uptake of dietary iron in the gut. This finding has implications for iron metabolism in other diseases and may contribute to the future development of therapies for thalassemia.


The study, led by researchers at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) at the NIH, appears online August 26, 2007, as an Advanced Online Publication in the journal, Nature Medicine.

Thalassemia is an inherited blood disease characterized by the under production of normal hemoglobin, the oxygen-carrying protein in red blood cells. People with severe forms of thalassemia often suffer from anemia, a condition in which the body tissues do not get enough oxygen from the blood, and often require blood transfusions.

Blood transfusions contribute to iron overload in people with thalassemia, but these people also suffer from iron overload independent of blood transfusions. Excess iron causes damage to many organs including the heart and liver, and diabetes can develop in severe cases. Patients with thalassemia often require treatment to remove the excess iron to prevent tissue damage.

"The treatment of iron overload in patients with thalassemia is particularly difficult because of their anemia," says Jeffery L. Miller, M.D., chief of the Molecular Genomics and Therapeutics Section of the Molecular Medicine Branch, Division of Intramural Research, NIDDK, and last author of the study. "So we have been searching for the mechanism responsible for iron overload in thalassemia in hopes of finding new therapies for those patients."


Thalassemia patients absorb too much iron from food due to abnormally low levels of a small peptide, called hepcidin, which regulates iron uptake from the gut. People with thalassemia should produce hepcidin at high levels. Instead, these patients have reduced levels of hepcidin. This confounded the authors and led them to ask if the low levels of hepcidin were somehow caused by the underlying problem in thalassemia -abnormal development of red blood cells.


Red blood cells, also called erythrocytes, are filled with hemoglobin, which transports oxygen throughout the body. Erythrocytes circulate in the blood, but they originate in the bone marrow as erythroblasts and go through several stages of differentiation until they finally leave the bone marrow and enter the blood stream as fully-formed erythrocytes.

Previous research has shown that people with thalassemia disorders have elevated numbers of erythroblasts in the bone marrow, but have reduced numbers of healthy erythrocytes circulating in the blood. Due to the problems with forming hemoglobin, many erythroblasts never make it into the blood stream as healthy erythrocytes.

"Since erythroblasts need iron to make hemoglobin, we reasoned that the increased number of erythroblasts in thalassemia may send stronger messages to the liver to suppress hepcidin and thereby absorb more iron even in the condition of iron overload,” says the study's lead author, Toshihiko Tanno, Ph.D., an investigator in Miller's laboratory in the NIDDK's Division of Intramural Research.

With this hypothesis in mind, Dr. Tanno set out to identify all the messages that are produced by adult stem cells, as they become erythroblasts and red blood cells. For this work, the team was able to examine all the genes expressed in those cells because a catalogue of those genes now exists based upon the NIH's Human Genome Project.

The authors identified growth differentiation factor 15 (GDF15) protein as being unusually elevated in people with thalassemia compared to healthy volunteers. Further study showed that GDF15 does indeed signal reduced hepcidin production in liver cells, and the study revealed additional erythroblast proteins that may be involved.

"We are continuing the search for other factors that regulate expression of hepcidin," says Miller. "We are also keenly interested in determining if the elevated levels of GDF15 cause other problems in thalassemia in addition to hepcidin suppression."

The team is now developing strategies to apply and translate their discovery into new diagnostic and therapeutic tools for the clinic. Drs. Miller and Tanno both agreed that while their discovery is a good start, the project will not be complete until the patients have benefited.

source: http://www.medindia.net/healthnews/Thalassemia-news.asp