Heparin: a potent inhibitor of hepcidin expression in vitro and in vivo

Abstract

Hepcidin is a major regulator of iron homeostasis, and its expression in liver is regulated by iron, inflammation, and erythropoietic activity with mechanisms that involve bone morphogenetic proteins (BMPs) binding their receptors and coreceptors. Here we show that exogenous heparin strongly inhibited hepcidin expression in hepatic HepG2 cells at pharmacologic concentrations, with a mechanism that probably involves bone morphogenetic protein 6 sequestering and the blocking of SMAD signaling. Treatment of mice with pharmacologic doses of heparin inhibited liver hepcidin mRNA expression and SMAD phosphorylation, reduced spleen iron concentration, and increased serum iron. Moreover, we observed a strong reduction of serum hepcidin in 5 patients treated with heparin to prevent deep vein thrombosis, which was accompanied by an increase of serum iron and a reduction of C-reactive protein levels. The data show an unrecognized role for heparin in regulating iron homeostasis and indicate novel approaches to the treatment of ironrestricted iron deficiency anemia. IntroductionIron maldistribution is implicated in various diseases, including hemochromatosis, iron-loading anemias, anemia of inflammation, and neurodegenerative disorders. 1 Body iron absorption and distribution are controlled by hepcidin, a small peptide secreted by hepatocytes that is expressed as a prepropeptide of 84 amino acids and is processed to the mature hormone of 25 residues by furin. 2,3 Hepcidin binds and induces the degradation of ferroportin, the only known cellular iron exporter, and thus it regulates iron absorption from duodenum and iron release from reticuloendothelial macrophages. 4 Inappropriately low levels of hepcidin are associated with the various forms of genetic hemochromatosis, 5 whereas high levels of hepcidin are found in inflammatory conditions, where they contribute to anemia. 6 Liver hepcidin expression is regulated by iron, erythropoietic activity, and inflammation, 6 with mechanisms that strongly rely on bone morphogenetic protein (BMP) signaling pathways. 7 Hemojuvelin, which is a main hepcidin regulator, acts as a BMP coreceptor, 8 and the modulation of its level by proteases tightly regulates hepcidin expression. 9,10 Hepcidin expression in hepatic cells is strongly stimulated by BMP2, BMP4, BMP6, and BMP9 11 and is reduced by inhibitors of the BMP/SMAD signaling pathway, such as noggin or dorsomorphin. 12 BMP6 is considered the physiologic BMP regulator of hepcidin because its expression is iron dependent and because BMP6 knockout mice demonstrate massive liver iron overload. 13,14 Hepcidin also is stimulated by the inflammatory cytokine interleukin-6 (IL-6) in a pathway that involves signal transducer and activator of transcription 3 (STAT3), [15][16][17] but it is dependent on the presence of SMAD4. 18 Methods to control hepcidin expression can be based on the modulation of BMP's activity. These proteins belong to the transforming growth factor-␤ family and exhibit a wide range of biologic effects on various cell types....

Disordered hepcidin–ferroportin signaling promotes breast cancer growth

“…Heparin was recently reported to be a potent inhibitor of liver-derived hepcidin production [27]. In pilot experiments, the qRT-PCR results indicated that hepcidin expression was suppressed in all 3 human hepatic cell lines, HepG2, SMMC-7721 and L-02 (by N50%, Fig.…”

Manipulation of the hepcidin pathway for therapeutic purposes

“…68 Poli and colleagues demonstrated that heparin inhibited hepcidin expression in hepatic cell lines as well as in mice. 69 Daily injections in mice for seven days (50 mg/kg/d) decreased hepcidin mRNA expression and SMAD phosphorylation, increased serum iron and reduced spleen iron concentration. In 5 patients treated with low molecular weight heparin to prevent deep vein thrombosis, serum hepcidin concentration decreased by 80-85% within 2-5 days after the start of the treatment.…”

“…To address this, Poli and colleagues recently prepared non-anticoagulant heparins 70 that retained BMP-modulating activity and potently suppressed hepcidin in vitro and in mice in vivo, also in the presence of an inflammatory stimulus. Interestingly, heparin is also known to have anti-inflammatory activity 69 and this could further contribute to its usefulness for the treatment of iron-restricted disorders.…”

Old and new applications of non-anticoagulant heparin

“…These and some N-acyl analogues showed beneficial effects in inflammation myocardial ischemic and reperfusion injury [5], inhibitory activity of angiogenesis and metastasis [89] in a broad spectrum of experimental models. An oversulfated LMWH preparation was found beneficial in an iron restricted anaemia model through inhibition of the peptide hormone Hepcidin [68]. Various types of derivatives, chemical processes, some biological interactions and activities are reported in dedicated reviews [87,89,92,93].…”

“…Allergic encephalomyelitis [5] Auto-immuno diseases [61] Anti-complement [29,62,63] Anti-atherosclerosis [64] Diabetic nephropathies [26,65] Emphysema [66,67] Iron-restricted anemia [68] Neuroprotection [60] Osteogenesis [69] Periodontal diseases [70] Cystic fibrosis b [80] Emphysema b Fraxiparine [81] Hematopoiesi c [82] Obstetrics c,e Dalteparin [83] Retinal angiogenesis c Suloparoid d [84] Ulcerative colitis c LMWHs [9] a Anecdotal trial; b experimental models; c clinical trials; d LMW heparan sulfate; e shorter human labor.…”