Hemopexin down-regulates LPS-induced proinflammatory cytokines from macrophages

Abstract

Detection of LPS in tissues is an integral component of innate immunity that acts to protect against invasion by Gram-negative bacteria. Plasma down-regulates LPS-induced cytokine production from macrophages, thereby limiting systemic inflammation in blood and distant tissues. To identify the protein(s) involved in this process, we used classical biochemical chromatographic techniques to identify fractions of mouse sera that suppress LPS-induced TNF from bone marrow-derived macrophages (BMDMs). Fractionation yielded microgram quantities of a protein that was identified by MS to be hemopexin (Hx). Mouse Hx purified on hemin-agarose beads and rhHx decreased the production of cytokines from BMDMs and peritoneal macrophages induced by LPS. Preincubation of LPS with Hx did not affect the activity of LPS on LAL, whereas preincubation of Hx with macrophages followed by washing resulted in decreased activity of these cells in response to LPS, suggesting that Hx acts on macrophages rather than LPS. Heme-free Hx did not stimulate HO-1 in the macrophages. Purified Hx also decreased TNF and IL-6 from macrophages induced by the synthetic TLR2 agonist Pam3Cys. Our data suggest that Hx, which is an acute-phase protein that increases during inflammation, limits TLR4 and TLR2 agonist-induced macrophage cytokine production directly through a mechanism distinct from HO-1.

Hemolysis and free hemoglobin revisited: exploring hemoglobin and hemin scavengers as a novel class of therapeutic proteins

“…81,82 The in vivo activity of Hpx may also involve Hpx activities that are independent of its primary hemin scavenger function. The outcome of such activities has been noted as anti-inflammatory in some cases (eg, Hpx attenuates inflammatory cytokine secretion by lipopolysaccharide-stimulated macrophages 83 ), whereas impaired bacterial clearance was found as a consequence of suppressed neutrophil migration in other mouse studies. 84 At this point, it is unknown whether such non-heminrelated effects of Hpx are an inherent activity of the protein itself or if they are side effects caused by impurities or degradation products in some preparations of plasma-derived Hpx.…”

MALDI-MSI and Ovarian Cancer Biomarkers

“…ApoA-I is known to decrease expression of surface molecules such as CD1a, CD80, CD86, and HLA-DR in dendritic cells, and it stimulates the production of IL-10 79 . Interestingly, hemopexin has recently been demonstrated to reduce TNF α and IL-6 from macrophages during inflammation and limits TLR4 and TLR2 agonist-induced macrophage cytokine production 80 . We demonstrate that in SKOV-3 epithelial ovarian carcinoma cells, all TLRs are over-expressed with the exception of TLR9 and TLR10 (Figure 6).…”

Kinetics and Specificity of Feline Leukemia Virus Subgroup C Receptor (FLVCR) Export Function and Its Dependence on Hemopexin

“…We demonstrate that the substrate specificity of FLVCR export involves heme and proximal planar porphyrins, but not bilirubin; that the export of heme is preferentially facilitated by hemopexin; and that hemopexin binds to FLVCR at a site thought to be important for heme export. A physiological role for hemopexin in heme iron recycling may explain the very high serum concentrations of hemopexin, 0.55-1.25 mg/ml (9.2-20.8 M) in mice (19) and 0.4 -1.5 mg/ml (6.7-25 M) in humans (20).…”