Hemin and a metabolic derivative coprohemin modulate the TLR4 pathway differently through different molecular targets.
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.
Piazza
Matteo
M
Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, Milan, Italy.
Damore
Gaetana
G
Costa
Barbara
B
Gioannini
Theresa L
TL
Weiss
Jerrold P
JP
Peri
Francesco
F
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
D004731:Endotoxins; D016209:Interleukin-8; D018950:Lipopolysaccharide Receptors; D051218:Lymphocyte Antigen 96; D051197:Toll-Like Receptor 4; C561849:coprohemin; D006427:Hemin
J Pharmacol Exp Ther. 1999 Oct;291(1):416-23
10490932
Proc Natl Acad Sci U S A. 2007 Feb 6;104(6):1919-24
17261807
Am J Pathol. 2001 Mar;158(3):893-903
11238038
Immunol Res. 2007;39(1-3):249-60
17917069
Artif Cells Blood Substit Immobil Biotechnol. 1994;22(2):207-13
8087243
J Biol Chem. 2007 Jul 13;282(28):20221-9
17502383
J Biol Chem. 2007 Jan 12;282(2):1010-7
17121827
Br J Haematol. 2006 Nov;135(3):281-92
16956347
J Neurosurg. 1993 Aug;79(2):252-5
8331409
Science. 1993 Jan 22;259(5094):522-5
8424176
J Biol Chem. 2000 Jul 7;275(27):20861-6
10877845
J Immunol. 2004 Apr 15;172(8):4926-33
15067072
Circ Res. 1999 Oct 15;85(8):663-71
10521239
J Exp Med. 2005 Jan 3;201(1):19-25
15630134
EMBO J. 1995 Jan 16;14(2):313-20
7835342
Blood. 1968 Nov;32(5):811-5
5687939
Proc Natl Acad Sci U S A. 2004 Mar 23;101(12):4186-91
15010525
Free Radic Res. 2000 Oct;33(4):341-8
11022843
Blood. 2001 Sep 15;98(6):1802-11
11535514
Proc Soc Exp Biol Med. 1997 Dec;216(3):456-63
9402154
Science. 1988 Apr 22;240(4851):433-9
3358128
Cell. 1989 Jan 27;56(2):291-301
2643482
Am J Pathol. 2000 May;156(5):1527-35
10793064
J Biol Chem. 2007 Mar 16;282(11):7877-84
17227775
Circulation. 2004 Feb 17;109(6):784-9
14970116
Blood. 2000 Jun 1;95(11):3442-50
10828027
Kidney Int. 1998 Jan;53(1):100-11
9453005
Pharmacol Rev. 2003 Sep;55(3):551-71
12869663
J Biol Chem. 2001 Feb 23;276(8):5883-91
11084043
J Biol Chem. 2002 Dec 6;277(49):47818-25
12372833