Hepatic Erythropoietin Production Research Articles

Drugs activating hypoxia-inducible factors correct erythropoiesis and hepcidin levels via renal EPO induction in mice

AbstractThe erythroid growth factor erythropoietin (EPO) is mainly produced by the kidneys in adult mammals and induces expansion of erythroid cells and iron use for hemoglobin synthesis. The liver also produces EPO at a lower level than the kidneys. Renal and hepatic EPO production is fundamentally regulated by hypoxia-inducible transcription factors (HIFs) in a hypoxia/anemia-inducible manner. Recently, small compounds that activate HIFs and EPO production in the kidneys by inhibiting HIF-prolyl hydroxylases (HIF-PHIs) have been launched to treat EPO-deficiency anemia in patients with kidney disease. However, the roles of the liver in the HIF-PHI–mediated induction of erythropoiesis and iron mobilization remain controversial. Here, to elucidate the liver contributions to the therapeutic effects of HIF-PHIs, genetically modified mouse lines lacking renal EPO-production ability were analyzed. In the mutant mice, HIF-PHI administration marginally increased plasma EPO concentrations and peripheral erythrocytes by inducing hepatic EPO production. The effects of HIF-PHIs on the mobilization of stored iron and on the suppression of hepatic hepcidin, an inhibitory molecule for iron release from iron-storage cells, were not observed in the mutant mice. These findings demonstrate that adequate induction of EPO mainly in the kidney is essential for achieving the full therapeutic effects of HIF-PHIs, which include hepcidin suppression. The data also show that HIF-PHIs directly induce the expression of duodenal genes related to dietary iron intake. Furthermore, hepatic EPO induction is considered to partially contribute to the erythropoietic effects of HIF-PHIs but to be insufficient to compensate for the abundant EPO induction by the kidneys.

Hypoxia-Inducible Factor Activators in Renal Anemia: Current Clinical Experience.

Prolyl hydroxylase domain oxygen sensors are dioxygenases that regulate the activity of hypoxia-inducible factor (HIF), which controls renal and hepatic erythropoietin production and coordinates erythropoiesis with iron metabolism. Small molecule inhibitors of prolyl hydroxylase domain dioxygenases (HIF-PHI [prolyl hydroxylase inhibitor]) stimulate the production of endogenous erythropoietin and improve iron metabolism resulting in efficacious anemia management in patients with CKD. Three oral HIF-PHIs-daprodustat, roxadustat, and vadadustat-have now advanced to global phase III clinical development culminating in the recent licensing of roxadustat for oral anemia therapy in China. Here, we survey current clinical experience with HIF-PHIs, discuss potential therapeutic advantages, and deliberate over safety concerns regarding long-term administration in patients with renal anemia.

Treatment of erythropoietin deficiency in mice with systemically administered siRNA

AbstractAnemia linked to a relative deficiency of renal erythropoietin production is a significant cause of morbidity and medical expenditures in the developed world. Recombinant erythropoietin is expensive and has been linked to excess cardiovascular events. Moreover, some patients become refractory to erythropoietin because of increased production of factors such as hepcidin. During fetal life, the liver, rather than the kidney, is the major source of erythropoietin. In the present study, we show that it is feasible to reactivate hepatic erythropoietin production and suppress hepcidin levels using systemically delivered siRNAs targeting the EglN prolyl hydroxylases specifically in the liver, leading to improved RBC production in models of anemia caused by either renal insufficiency or chronic inflammation with enhanced hepcidin production.

Liver Specific Delivery of siRNA Targeting EGLN Prolyl Hydroxylases Activates Hepatic Erythropoietin Production and Stimulates Erythropoiesis,

Abstract 3161Anemia in chronic kidney disease patients due to impaired renal production of erythropoietin (EPO) and insufficient erythropoiesis is a significant public health problem. One approach to compensate for the low EPO levels in patients with impaired kidney function would be to stimulate the levels of EPO production from non-renal sources. It is well known that during fetal development the liver serves as the primary producer of EPO until the kidney becomes the dominant source after birth. Negative regulation of EPO production is mediated by the EGLN family of prolyl hydroxylases (PHDs1-3) that play an important role in oxygen sensing by targeting the transcription factor hypoxia inducible factor (HIF) for degradation via the proteasome. HIF stabilization and activity is required to mediate EPO gene transcription. Previously it has been shown that liver specific conditional knockout of all three PHDs is required to activate HIF and induce EPO production in liver (Minamishima et al. Science 2010). Here we show that simultaneous siRNA mediated knockdown of all 3 PHD genes in mouse liver using lipid nanoparticles (LNPs) can induce hepatic EPO mRNA activation, elevation of serum EPO levels and stimulation of erythropoiesis. We extend these data by examining siRNA knockdown of different combinations of the 3 PHD genes and demonstrate that PHD2 is the dominant PHD gene regulating hepatic EPO production. In addition, due to the specificity of the LNP delivery system we show that the HIF activation and increase in EPO mRNA occurs specifically in liver. Increases in serum EPO and hematocrit were durable for two weeks and one month after a single intravenous dose of LNP siRNA. Furthermore, PHD siRNA silencing in a 5/6 nephrectomy model successfully elevates hemoglobin levels and corrects anemia. In conclusion, targeting of EGLN prolyl hydroxylase genes with siRNA therapeutics has potential in the treatment of anemia associated with chronic kidney disease and provides liver-specific target gene regulation. Disclosures:Querbes:Alnylam Pharmaceuticals: Employment. Bogorad:Alnylam Pharmaceuticals: Research Funding. Moslehi:Alnylam Pharmaceuticals: Honoraria. Akinc:Alnylam Pharmaceuticals: Employment. Wong:Alnylam Pharmaceuticals: Employment. Zurenko:Alnylam Pharmaceuticals: Employment. Qin:Alnylam Pharmaceuticals: Employment. Hettinger:Alnylam Pharmaceuticals, Inc.: Employment. Kuchimanchi:Alnylam Pharmaceuticals: Employment. Charisse:Alnylam Pharmaceuticals: Employment. Sah:Alnylam Pharmaceuticals, Inc.: Employment. Fitzgerald:Alnylam Pharmaceuticals: Employment. Kotelianski:Alnylam Pharmaceuticals: Employment. Kaelin:Fibrogen: Consultancy, Equity Ownership.

Reactivation of hepatic EPO synthesis in mice after PHD loss.

The kidney controls erythropoietin production in adults, and the anemia that can accompany renal failure is a major medical problem. The liver controls erythropoietin production during fetal life but is silenced shortly after birth. Erythropoietin transcription is controlled by hypoxia-inducible factor (HIF), which is inhibited by three prolyl hydroxylases (PHD1, PHD2, and PHD3). Systemic PHD2 inactivation has been found to increase renal, but not hepatic, erythropoietin production. In contrast, we show here that simultaneous genetic inactivation of all three PHD paralogs in mice reactivates hepatic erythropoietin production and stimulates red blood synthesis, suggesting that pan-PHD inhibitory drugs might be useful for the treatment of anemia caused by chronic kidney disease.

Axitinib Induces Paradoxical Erythropoietin Synthesis in Metastatic Renal Cell Carcinoma

TO THE EDITOR: In a recent letter, Alexandrescu et al reported thoughtful data to address the occurrence of erythrocytosis after treatment with tyrosine kinase inhibitors (TKIs) sorafenib and sunitinib for metastatic cancers. In addition, it has been previously reported that patients with von Hippel-Lindau (VHL) disease treated with semaxanib, a TKI targeting vascular endothelial growth factor receptor 2 (VEGFR-2) and cKit, may experience a supra-additive increase in hematocrit level. Experimental studies showing hepatic erythropoietin (EPO) synthesis related to VEGF blockage could explain this iatrogenic polycythemia. We report a case of polycythemia in a patient treated for metastatic renal cell carcinoma with axitinib, another TKI targeting VEGFR-2. Our findings were the opposite of those in the report by Alexandrescu et al. A 52-year-old man, with no significant past medical history, underwent a right radical nephrectomy for clear renal cell carcinoma. In October 2002, a partial response was achieved with interferon-alfa treatment for lung metastases. In March 2004, the lung metastases progressed in number and size, and the patient subsequently was enrolled onto an axitinib phase II trial. Oral axitinib was administered continuously at the fixed dose of 5 mg twice daily. Minor adverse effects were reported, including diarrhea and asthenia. During the initiation of the second cycle (week 5), we observed an increase in hematocrit, which was confirmed during the subsequent cycles. An isotopic measurement of RBCs confirmed the diagnosis of polycythemia. Treatment was continued for 36 months, with a documented complete response by the third cycle. However, repeated therapeutic phlebotomies for polycythemia remained necessary. There was no alternative cause of polycythemia, including the absence of clinical evidence of VHL disease. In addition, no somatic VHL mutation in the tumor sample was found in polymerase chain reaction analysis. Endogenous EPO blood levels and VEGF-A levels were monitored, and results are listed in Table 1. Tam et al demonstrated that erythropoiesis is regulated by endogenous VEGF. In Tam’s preclinical study, high-grade VEGF blockage induced the repression of adult hepatic EPO production. The absence of VEGFR-2 expression on hepatocytes suggests the participation of liver sinusoidal endothelial cells with homeostatic VEGFR-2– dependant paracrine signaling. In our observation, axitinib treatment was associated with a paradoxical VEGF increase, as reported both in vivo and in a cohort of patients with metastatic gastrointestinal stromal tumors treated with sunitinib, another TKI with VEGFR-2 inhibition. However, we speculate that axitinib mimics VEGF starvation in organs (such as the liver) through VEGFR-2 blockade, and leads to hepatic EPO production. Finally, we cannot exclude an axitinib interaction with the hypoxiainducible factor pathway, which induces nitric oxide release, cutaneous vascular flow modification, and increased systemic EPO expression. Further investigation in clinical trials is warranted to determine the utility of EPO blood level as a marker of VEGF/ VEGFR modulator activity.

Erythropoietin-Producing Cells in the Liver of ICR-Derived Glomerulonephritis (ICGN) Mice

The ICR-derived glomerulonephritis (ICGN) mouse is an appropriate model for anemia associated with chronic renal disorder (CRD). Insufficient renal production of erythropoietin (EPO) induces the anemia associated with CRD. EPO mRNA is expressed in both kidneys and liver of progressing-stage ICGN mice. Hypoxic stimulation induced the EPO mRNA expression in the liver as well as in the kidneys of ICGN mice. The localization of EPO-producing cells in the liver remains controversial. Present study using an amplified in situ hybridization technique identified that nonparenchymal cells were the source of hepatic EPO production in ICGN mice under both normoxia and hypoxia.

Hypoxia-Independent Regulation of Hepatic Erythropoietin Production by Vascular Endothelial Growth Factor.

Erythropoietin (Epo) is an essential regulator of red blood cell production. While adult Epo synthesis occurs almost exclusively in kidney, extrarenal Epo synthesis has been described in liver and brain in response to hypoxia or anemia. We have used adenoviruses to express soluble ectodomains of the VEGF receptors (sVEGFRs) Flk1 and Flt1 in the circulation of mice, achieving high-level VEGF sequestration, potent conditional ablation of VEGF function in adult animals, and inhibition of tumor growth and angiogenesis (Kuo et al. PNAS (2001). 98: 4605). Intriguingly, adenoviral expression of soluble Flk1 or Flt1 ectodomains, or a recently described soluble receptor VEGF Trap, is associated with profound stimulation of erythropoiesis and polycythemia, with hematocrit as high as 75% from basal levels of ~45%, and elevation of plasma Epo levels. sVEGFR expression results in a profound >100-fold induction of hepatic erythropoietin synthesis while renal Epo production is completely repressed. This effect is specific for adenoviruses expressing soluble VEGF receptors and not other receptor ectodomains, does not require liver transduction or hypoxia, and is not affected by Ad Cre-induced deletion of the hepatocyte HIF-1a gene in HIF-1aflox/flox mice. Selective inhibition of hepatocyte-produced VEGF in Ad Cre-treated VEGFflox/flox mice is sufficient to re-activate hepatocyte Epo production, likely via hepatocyte × endothelium crosstalk. These data suggest VEGF may function physiologically to repress hepatic Epo synthesis, while VEGF blockade leads to de-repression of hepatic Epo production via a novel hypoxia- and HIF-1a-independent pathway.

Tumor necrosis factor p55 receptor (TNF-RI) mediates the in vitro inhibition of hepatic erythropoietin production

Tumor necrosis factor α (TNFα) is thought to contribute to the blunted erythropoietin (Epo) production in inflammatory diseases. The present study was carried out to find out as to whether the 55 kD (TNF-RI) or the 75 kD (TNF-RII) receptor is responsible for the TNFα-induced inhibition of hepatic Epo synthesis. When the effects of two receptor-specific mutants were compared, only the TNF-RI-specific isoform proved to suppress the formation of immunoreactive Epo in the human hepatoma cell lines HepG2 and Hep3B, similar to the effect of wild-type TNFα. Anti-TNFα antibody restored Epo production in TNFα- or TNF-RI mutant-treated cultures. By gel shift assay NF-κB binding to DNA was demonstrated following the addition of TNFα or TNF-RI-specific mutant to HepG2 cells, while the TNF-RII-specific mutant was ineffective. Finally, immunoreactive TNF-RI, but not TNF-RII, fragments were measurable in cell culture supernatants. Taken together, these results suggest that the inhibition of hepatic Epo production by TNFα is mediated by TNF-RI signaling.

Cellular sites of extrarenal and renal erythropoietin production in anaemic rats.

The cellular origins of erythropoietin were investigated in the rat using a probe derived from a cloned rat erythropoietin cDNA. In anaemic-hypoxic rat liver, in situ hybridization detected erythropoietin mRNA primarily in hepatocytes and less frequently in nonparenchymal sinusoidal or perisinusoidal liver cells. An RNase protection assay was used to compare the erythropoietin mRNA contents of separated rat liver cell fractions and also suggested that hepatocytes are the major source of extrarenal erythropoietin with nonparenchymal liver cells contributing less than 1% to total hepatic erythropoietin production. In kidney, in situ hybridization localized erythropoietin mRNA in nonepithelial cells, as yet of undefined lineage, in the cortical and outer medullary interstitium. These results indicate that, in the rat, the primary sources of erythropoietin in liver and kidney are different types of cells.

Polycythemia and the Budd-Chiari syndrome: study of serum erythropoietin and bone marrow erythroid progenitors.

The mechanism of polycythemia associated with the Budd-Chiari syndrome is unknown. Erythropoiesis in 10 patients with Budd-Chiari syndrome was studied in an attempt to distinguish prior unrecognized polycythemia vera from secondary polycythemia. Serum erythropoietin was assayed using a mouse fetal liver erythroblast assay. High concentrations of serum erythropoietin were observed in 6 of 7 patients with acute primary Budd-Chiari syndrome. Levels were normal in four patients who were investigated during the chronic phase and were increased in one with persisting polycythemia. In one patient, erythropoietin concentration in the hepatic vein was twice the level measured in peripheral, caval and renal venous blood. Bone marrow erythroid progenitors developed in vitro in the absence of exogenous erythropoietin in all polycythemia vera cases studied in acute and chronic phases, whether polycythemia persisted or not. These findings indicate that hepatic erythropoietin production occurs in the acute phase of Budd-Chiari syndrome and suggest that, in some cases of Budd Chiari syndrome, polycythemia which resolves after the acute phase may be secondary to liver disease.

Hepatic regeneration and erythropoietin production in the rat.

The regenerating liver produces erythropoietin in response to hypoxia. The amounts of erythropoietin produced in animals subjected to hepatectomy are significantly higher than those observed in sham-operated animals. Hepatic erythropoietin production appears to be dependent upon the stage of regeneration with the highest levels being produced during the period of greatest proliferation and increase in liver mass.

Hepatic Erythropoietin Production in the Lead-poisoned Rat

Abstract Extrarenal erythropoietin production is increased above normal in lead-injected rats exposed to hypoxia either immediately after or 1 day after nephrectomy. Extrarenal erythropoietin production in lead-poisoned rats is actinomycin D sensitive, and the major extrarenal site of production or activation of the hormone in normal or lead-poisoned anephric rats is the liver.