Hexa-d-arginine (D6R), a poly-arginine, inhibited both LT-induced macrophage lysis and PA83 cleavage [63] D6R-protected Fisher rats and FVB and 129/SV mice from LT challenge. 2009 [4,6-10]. Unfortunately, in these anthrax outbreaks the development of septic shock has been associated with a particularly poor prognosis despite patients receiving aggressive conventional therapy with antibiotics and intensive care support. All patients with shock during the US 2001 outbreak died [2,5,11]. A review of 27 confirmed cases of infection from the outbreak in injection drug users in the UK noted that the mortality rate among patients requiring vasopressor therapy was close to 80% and substantially higher than other types of septic shock [4,12,13]. These findings emphasize the need to identify adjunctive therapies, which can be used with conventional ones to improve outcomes. produces two toxins, lethal toxin and edema toxin (LT and ET), strongly implicated in its associated shock and lethality and which are likely targets for adjunctive therapies [1,14-16]. Over the past 10 C 15 years, there has been considerable progress identifying agents with the potential to therapeutically inhibit LT and ET. Here, we first briefly discuss the structure, actions and cardiovascular effects of LT and ET. We then describe the steps required for toxin uptake by host cells and in that context, discuss agents which have been identified with the potential to serve as or be developed into adjunctive therapies for anthrax. 2. toxin structure, Isosilybin A function and potential cardiovascular effects LT and ET are binary toxins comprised of protective antigen (PA), a protein that mediates the uptake of the toxins’ toxic moieties: lethal factor (LF) for LT and edema factor (EF) for ET [17,18]. LF is a zinc-dependent metalloprotease which inactivates MAPKK 1 C 4 and 6 and essential stress kinase pathways [19]. LF also activates the Nlrp-1 inflammasome in macrophages and dendritic cells, resulting in caspase-1 activation, IL-1 and IL-18 production, and cell death [20]. EF has potent calmodulin-dependent adenyl cyclase activity and rapidly increases intracellular cAMP levels [21]. Data in and models suggest that LT can disrupt endothelial barrier function and produce hypotension in part through the extravasation of fluid [1,2]. Some studies have also suggested that LT, but not ET, may have direct myocardial depressant effects, while others have not [22]. Other studies have suggested that ET also has a direct effect on reducing endothelial barrier function and can produce intravascular volume losses [1,2]. On the one hand, this would be consistent with ET’s known ability to produce localized tissue edema when injected subcutaneously in animals. Notably though, endothelial impairment is not consistent with EF’s recognized action Rabbit Polyclonal to Chk2 (phospho-Thr387) of potent adenyl cyclase activity since much research has shown that increased intracellular cAMP levels have potential endothelial-protective effects [23,24]. Alternatively, ET may produce shock by causing direct arterial and venous relaxation and dilation, changes very consistent with its adenyl cyclase activity [22,25]. 3. Toxin uptake during infection During infection, PA protomers with a molecular weight (MW) of 83 (PA83) bind to host cells via one of two receptors, tumor endothelial marker 8 (TEM8) or capillary morphogenesis gene-2 (CMG2) (Figure 1) [17,18,26-28]. Both receptors express an extracellular von Willebrand factor A (vWA) domain that binds to PA83 and are present in a wide variety of tissues. CMG2 may have a greater role in infection due to its higher affinity for PA. A third possible toxin receptor with a vWA domain has been implicated in toxin uptake but its pathogenic contribution Isosilybin A is unclear [29]. Following host cell binding, the PA83 protomer undergoes furin cleavage into an active 63 kDa monomer and inactive 20 kDa monomer (PA63 and PA20) [30]. The small monomers are released while the PA63 monomers oligomerize into heptamers or octamers, termed prepores, which localize to lipid raft regions of the cell membrane. The formation of the prepore oligomers results in their activation and ability to bind three to four LF or EF molecules and to undergo endocytosis. As the endosome is internalized, decreasing intravesicular pH stimulates prepore incorporation into the endosomal. Isosilybin A