Bacillus anthracis edema toxin inhibits Staphylococcus aureus enterotoxin B effects in vitro: a potential protein therapeutic?

Anthrax edema toxin has cAMP-mediated stimulatory effects and high-dose lethal toxin has depressant effects in an isolated perfused rat heart model

While anthrax edema toxin produces pronounced tachycardia and lethal toxin depresses left ventricular (LV) ejection fraction in in vivo models, whether these changes reflect direct cardiac effects as opposed to indirect ones related to preload or afterload alterations is unclear. In the present study, the effects of edema toxin and lethal toxin were investigated in a constant pressure isolated perfused rat heart model. Compared with control hearts, edema toxin at doses comparable to or less than a dose that produced an 80% lethality rate (LD(80)) in vivo in rats (200, 100, and 50 ng/ml) produced rapid increases in heart rate (HR), coronary flow (CF), LV developed pressure (LVDP), dP/dt(max), and rate-pressure product (RPP) that were most pronounced and persisted with the lowest dose (P ≤ 0.003). Edema toxin (50 ng/ml) increased effluent and myocardial cAMP levels (P ≤ 0.002). Compared with dobutamine, edema toxin produced similar myocardial changes, but these occurred more slowly and persisted longer. Increases in HR, CF, and cAMP with edema toxin were inhibited by a monoclonal antibody blocking toxin uptake and by adefovir, which inhibits the toxin's intracellular adenyl cyclase activity (P ≤ 0.05). Lethal toxin at an LD(80) dose (50 ng/ml) had no significant effect on heart function but a much higher dose (500 ng/ml) reduced all parameters (P ≤ 0.05). In conclusion, edema toxin produced cAMP-mediated myocardial chronotropic, inotropic, and vasodilatory effects. Vasodilation systemically with edema toxin could contribute to shock during anthrax while masking potential inotropic effects. Although lethal toxin produced myocardial depression, this only occurred at high doses, and its relevance to in vivo findings is unclear.

Synthesis and assembly of a full-length human monoclonal antibody in algal chloroplasts

Monoclonal antibodies can be effective therapeutics against a variety of human diseases, but currently marketed antibody-based drugs are very expensive compared to other therapeutic options. Here, we show that the eukaryotic green algae Chlamydomonas reinhardtii is capable of synthesizing and assembling a full-length IgG1 human monoclonal antibody (mAb) in transgenic chloroplasts. This antibody, 83K7C, is derived from a human IgG1 directed against anthrax protective antigen 83 (PA83), and has been shown to block the effects of anthrax toxin in animal models. Here we show that 83K7C heavy and light chain proteins expressed in the chloroplast accumulate as soluble proteins that assemble into complexes containing two heavy and two light chain proteins. The algal-expressed 83K7C binds PA83 in vitro with similar affinity to the mammalian-expressed 83K7C antibody. In addition, a second human IgG1 and a mouse IgG1 were also expressed and shown to properly assemble in algal chloroplast. These results show that chloroplasts have the ability to fold and assemble full-length human mAbs, and suggest the potential of algae as a platform for the cost effective production of complex human therapeutic proteins.

New insights into the pathogenesis and treatment of anthrax toxin-induced shock

Inhalational Bacillus anthracis infection is a leading bioterrorist health threat in the US today. Lethal (LeTx) and edema toxin production are key to the virulent effects of this lethal bacteria. Recent insights into the structure and function of these toxins have increased the understanding of both the pathogenesis and treatment of anthrax. These are binary type toxins comprised of protective antigen necessary for their cellular uptake and either lethal or edema factors, the toxigenic moieties. Primary cellular receptors for protective antigen have been identified and the processing of the completed toxins clarified. Consistent with the ability of lethal factor to cleave mitogen activated protein kinase kinases, the evidence indicates that an excessive inflammatory response does not contribute to shock with LeTx. Rather, the immunosuppressive effects of LeTx could promote infection; however, direct endothelial dysfunction may have an important role in shock due to LeTx. Recent studies show that edema factor, a potent adenyl cyclase, may have a major role in shock during anthrax and that it may also be immunosuppresive. Therapies under development which target several steps in the cellular uptake and function of these two toxins have been effective in both in vitro and in vivo systems. Understanding how best to apply these agents in combination with conventional treatments should be a goal of future research.

Lethal and edema toxins in the pathogenesis of Bacillus anthracis septic shock: implications for therapy

Recent research regarding the structure and function of Bacillus anthracis lethal (LeTx) and edema (ETx) toxins provides growing insights into the pathophysiology and treatment of shock with this lethal bacteria. These are both binary-type toxins composed of protective antigen necessary for their cellular uptake and either lethal or edema factors, the toxigenic moieties. The primary cellular receptors for protective antigen have been identified and constructed and key steps in the extracellular processing and internalization of the toxins clarified. Consistent with the lethal factor's primary action as an intracellular endopeptidase targeting mitogen-activated protein kinase kinases, growing evidence indicates that shock with this toxin does not result from an excessive inflammatory response. In fact, the potent immunosuppressive effects of LeTx may actually contribute to the establishment and persistence of infection. Instead, shock with LeTx may be related to the direct injurious effects of lethal factor on endothelial cell function. Despite the importance of LeTx, very recent studies show that edema factor, a potent adenyl cyclase, has the ability to make a substantial contribution to shock caused by B. anthracis and works additively with LeTx. Furthermore, ETx may contribute to the immunosuppressive effects of LeTx. Therapies under development that target several different steps in the cellular uptake and function of these two toxins have been effective in in vitro and in vivo systems. Understanding how best to apply these agents clinically and how they interact with conventional treatments should be goals for future research.