Summary
In addition to their anticoagulant activity,unfractionated heparin (UFH) and low-molecular-weight
heparin (LMWH) have important immunomodulatory properties. However, different studies
have reported conflicting pro- and anti-inflammatory effects in association with heparin.
Moreover, the molecular basis for these heparin effects on inflammation remains unclear.It
was the objective of this study to determine how UFH and LMWH regulate lipopolysaccharide
(LPS)-induced activation of human mononuclear cells in whole blood, and define the
role of lipopolysaccharide- binding protein (LBP) in mediating this effect. Whole
blood was pre-treated with UFH or LMWH (0.1–200 IU/ml), prior to stimulation with
LPS (10 ng/ml). After six hours, monocyte pro-inflammatory cytokine (interleukin (IL)-1β,
IL-6, IL-8, and TNF-α) secretion was determined by plasma ELISA. Parallel experiments
using THP-1 cell line and primary monocytes were performed under serum-free conditions,
in the presence or absence of LBP (50–100 nM). Under serum-free conditions, heparin
demonstrated dose-dependent anti-inflammatory effects,significantly reducing secretion
of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, and TNF-α) in response to LPSstimulation
of THP-1 cells and primary monocytes. In contrast, in the presence of LBP, both UFH
and LMWH demonstrated dose-dependent pro-inflammatory effects at all heparin concentrations.
In ex-vivo whole blood experiments, pro-inflammatory effects (increased IL-1β and
IL-8 following LPS-stimulation) of heparin were also observed,but only at supra-therapeutic
doses (10–200 IU/ml). Our data demonstrate that in the absence of LBP, the direct
effect of heparin on LPS-stimulated monocytes is anti-inflammatory. However in whole
blood, the immunomodulatory effects of heparin are significantly more complex, with
either pro- or anti-inflammatory effects dependent upon heparin concentration.
Keywords
Heparins - inflammation - inflammatory mediators
