In that study systemically administered heparin, however, did not alter pulmonary coagulopathy. Here we show that all nebulized agents limit pulmonary coagulopathy to a similar extent.rh-aPC exerts profibrinolytic effects through inactivation of PAI-1 [38]. In our experiments reduction of PAI-1 activity in the rh-aPC-treated rats was, however, not sufficient to influence bronchoalveolar PAA. that Interestingly, plasma-derived AT affected PAI-1 activity, as well as bronchoalveolar PAA. To our knowledge, no direct effects of AT have been described that account for such alterations in these fibrinolytic markers. It is possible that these changes are due to the reduction in bacterial load observed in the plasma-derived AT-treated rats.In vitro experimentsThe in vitro experiments confirmed, at least in part, the findings of the in vivo animal study.

Indeed, bacterial outgrowth in BALF from rats treated with plasma-derived AT was reduced when compared with BALF from placebo-treated animals. Our experiment with TSB medium with different concentrations of plasma-derived AT showed this was not caused by a direct antibacterial effect of AT. During infection, innate host immune responses can lead to the expression of cationic antimicrobial peptides [23]. Such peptides can be inhibited by nonspecific binding to negatively charged parts of molecules such as coagulation products and other extracellular proteins. We hypothesize that the reduced bacterial outgrowth seen in our in vivo experiments might have been due to the fact that plasma-derived AT reduced total protein levels in the BALF by a factor of 10 compared with placebo-treated rats, thereby reducing the nonspecific inhibitory effects on cationic antimicrobial peptides.

Neutralizing these cationic antimicrobial peptides with SPS then should attenuate the possible inhibitory effect of BALF-AT on S. pneumoniae. Indeed adding SPS to BALF-AT diminished its inhibitory effect on the outgrowth of S. pneumoniae after six hours. This finding implies that the induction of coagulation by S. pneumoniae serves to protect the bacteria against cationic antimicrobial components, most likely innate host defense peptides, and thus can be considered a novel virulence mechanism. However, because the present study treatment with rh-aPC resulted in quite similar anticoagulant and profibrinolytic effects, while at the same time not affecting bacterial outgrowth or ALI, other mechanisms than anticoagulation may be responsible for the effects of plasma-derived AT found.

Details of these mechanisms are presently under investigation.LimitationsOur animal study has some important limitations. AV-951 First, the chosen dosages for each anticoagulant agent are determined based on data from previous studies and pilot studies combined with the efficacy of our nose-only exposure system, and possibility of dissolving each agent to an acceptable volume for nebulization.