Abstract:
It is well known that a variety of inflammatory diseases are accompanied by
hypercoagulability, and a number of more-or-less longer-term signalling pathways
have been shown to be involved. In recent work, we have suggested a
direct and primary role for bacterial lipopolysaccharide (LPS) in this hypercoagulability,
but it seems never to have been tested directly. Here, we show
that the addition of tiny concentrations (0.2 ng l21) of bacterial LPS to both
whole blood and platelet-poor plasma of normal, healthy donors leads to
marked changes in the nature of the fibrin fibres so formed, as observed by
ultrastructural and fluorescence microscopy (the latter implying that the
fibrin is actually in an amyloid b-sheet-rich form that on stoichiometric
grounds must occur autocatalytically). They resemble those seen in a
number of inflammatory (and also amyloid) diseases, consistent with an involvement
of LPS in their aetiology. These changes are mirrored by changes in
their viscoelastic properties as measured by thromboelastography. As the
terminal stages of coagulation involve the polymerization of fibrinogen into
fibrin fibres, we tested whether LPS would bind to fibrinogen directly. We
demonstrated this using isothermal calorimetry. Finally, we show that these
changes in fibre structure are mirrored when the experiment is done simply
with purified fibrinogen and thrombin (+0.2 ng l21 LPS). This ratio of concentrations
of LPS : fibrinogen in vivo represents a molecular amplification by the
LPS of more than 108-fold, a number that is probably unparalleled in biology.
The observation of a direct effect of such highly substoichiometric amounts of
LPS on both fibrinogen and coagulation can account for the role of very small
numbers of dormant bacteria in disease progression in a great many inflammatory
conditions, and opens up this process to further mechanistic analysis and
possible treatment.
