title: Hemin and a metabolic derivative coprohemin modulate the TLR4 pathway differently through different molecular targets.
abstract: Heme is a prosthetic group in a large number of essential proteins that have a pivotal role in oxygen transport, storage and electron shuttling. High amounts of free heme are associated with pathological states. Recently, it has been suggested that activation of Toll-like receptor 4 (TLR4) is one of the ways in which the 'danger signal' of free heme is detected. Here, we examine the biochemical basis of the modulation of the TLR4 pathway by hemin (iron(III)-protoporphyrin IX) and its metabolic, oxidated derivative coprohemin (iron(III)-coproporphyrin I). High concentrations of hemin (50 μM) triggered TLR4-mediated IL-8 production in the human HEK293/TLR4 cell line in the absence of the co-receptors CD14 and MD-2; the latter an essential co-receptor for TLR4 activation by endotoxin. Hemin and endotoxin have additive effects when co-administrated to HEK/TLR4 cells, suggesting that hemin and endotoxin activate TLR4 by different mechanisms. Coprohemin, in contrast to hemin, is unable to trigger TLR4-dependent activation of HEK/TLR4 cells, but instead causes dose-dependent inhibition of endotoxin-stimulated IL-8 production. The inhibitory effect of coprohemin is paralleled by reduced delivery of endotoxin to MD-2 (-TLR4) that is necessary for activation of TLR4 by endotoxin. Thus, despite their similar chemical structure, hemin and coprohemin have very different effects on the TLR4 pathway, the former acting as a mild agonist of TLR4, the latter as an antagonist selectively targeting the endotoxin-MD-2 interaction.
authors.affiliation: Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Piazza
authors.forename: Gaetana
authors.initials: G
authors.lastname: Damore
authors.forename: Barbara
authors.initials: B
authors.lastname: Costa
authors.forename: Theresa L
authors.initials: TL
authors.lastname: Gioannini
authors.forename: Jerrold P
authors.initials: JP
authors.lastname: Weiss
authors.forename: Francesco
authors.initials: F
authors.lastname: Peri
mesh_terms: D004731:Endotoxins / Q000494:pharmacology; D057809:HEK293 Cells; D006427:Hemin / Q000031:analogs & derivatives / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007113:Immunity, Innate; D016209:Interleukin-8 / Q000096:biosynthesis / Q000235:genetics; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D051218:Lymphocyte Antigen 96 / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000819:agonists* / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D004731:Endotoxins; D016209:Interleukin-8; D018950:Lipopolysaccharide Receptors; D051218:Lymphocyte Antigen 96; D051197:Toll-Like Receptor 4; C561849:coprohemin; D006427:Hemin
references.citation: J Pharmacol Exp Ther. 1999 Oct;291(1):416-23
references.pmid: 10490932
references.citation: Proc Natl Acad Sci U S A. 2007 Feb 6;104(6):1919-24
references.pmid: 17261807
references.citation: Am J Pathol. 2001 Mar;158(3):893-903
references.pmid: 11238038
references.citation: Immunol Res. 2007;39(1-3):249-60
references.pmid: 17917069
references.citation: Artif Cells Blood Substit Immobil Biotechnol. 1994;22(2):207-13
references.pmid: 8087243
references.citation: J Biol Chem. 2007 Jul 13;282(28):20221-9
references.pmid: 17502383
references.citation: J Biol Chem. 2007 Jan 12;282(2):1010-7
references.pmid: 17121827
references.citation: Br J Haematol. 2006 Nov;135(3):281-92
references.pmid: 16956347
references.citation: J Neurosurg. 1993 Aug;79(2):252-5
references.pmid: 8331409
references.citation: Science. 1993 Jan 22;259(5094):522-5
references.pmid: 8424176
references.citation: J Biol Chem. 2000 Jul 7;275(27):20861-6
references.pmid: 10877845
references.citation: J Immunol. 2004 Apr 15;172(8):4926-33
references.pmid: 15067072
references.citation: Circ Res. 1999 Oct 15;85(8):663-71
references.pmid: 10521239
references.citation: J Exp Med. 2005 Jan 3;201(1):19-25
references.pmid: 15630134
references.citation: EMBO J. 1995 Jan 16;14(2):313-20
references.pmid: 7835342
references.citation: Blood. 1968 Nov;32(5):811-5
references.pmid: 5687939
references.citation: Proc Natl Acad Sci U S A. 2004 Mar 23;101(12):4186-91
references.pmid: 15010525
references.citation: Free Radic Res. 2000 Oct;33(4):341-8
references.pmid: 11022843
references.citation: Blood. 2001 Sep 15;98(6):1802-11
references.pmid: 11535514
references.citation: Proc Soc Exp Biol Med. 1997 Dec;216(3):456-63
references.pmid: 9402154
references.citation: Science. 1988 Apr 22;240(4851):433-9
references.pmid: 3358128
references.citation: Cell. 1989 Jan 27;56(2):291-301
references.pmid: 2643482
references.citation: Am J Pathol. 2000 May;156(5):1527-35
references.pmid: 10793064
references.citation: J Biol Chem. 2007 Mar 16;282(11):7877-84
references.pmid: 17227775
references.citation: Circulation. 2004 Feb 17;109(6):784-9
references.pmid: 14970116
references.citation: Blood. 2000 Jun 1;95(11):3442-50
references.pmid: 10828027
references.citation: Kidney Int. 1998 Jan;53(1):100-11
references.pmid: 9453005
references.citation: Pharmacol Rev. 2003 Sep;55(3):551-71
references.pmid: 12869663
references.citation: J Biol Chem. 2001 Feb 23;276(8):5883-91
references.pmid: 11084043
references.citation: J Biol Chem. 2002 Dec 6;277(49):47818-25
references.pmid: 12372833