Bacillus anthracis Edema and Lethal Toxin Have Different Hemodynamic Effects but Function Together to Worsen Shock and Outcome in a Rat Model
1Critical Care Medicine Department, Clinical Center, and 2National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, and 3Human Genome Sciences, Rockville, Maryland
Introduction. To better define the contribution of edema toxins (ETx) and lethal toxins (LeTx) to shock with Bacillus anthracis, recombinant preparations of each were investigated alone or together in rats.
Methods and results. Lethal dose ranges (0%–100% lethality) of ETx (200–800 μg/kg as a 24-h infusion) were higher than those of LeTx (12.5–200 μg/kg) (
). However, compared with LeTx, similarly lethal ETx doses produced earlier and greater reductions in mean blood pressure (MBP) and increased, rather than decreased, heart rate (HR) (
for all). Combining either similar weight or lethal doses of ETx and LeTx increased the hazard ratio for death (log ± standard error) similar to the sum calculated with the toxin's effects alone (
observed vs.
calculated for similar weight and
vs.
for similar lethal doses;
for both). Early (
10 h) and late during infusion, ETx and LeTx together also altered MBP and HR in patterns consistent with the sum of their individual effects.
Conclusions. ETx was
10 times less lethal than LeTx but produced greater hypotension and added to the latter's harmful effects. These findings suggest that it may be appropriate for antitoxin therapies for B. anthracis to target both ETx and LeTx.
Received 22 June 2006; accepted 22 August 2006; electronically published 3 January 2007.
Cited by
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Potential conflicts of interest: M.S. owns stock options and is an employee of Human Genome Sciences. M.W.L. owns stock in and is a former employee of Human Genome Sciences. All other authors report no conflicts.
Presented in part: American Thoracic Society meeting, San Diego, 19–24 May 2006 (abstract A803, poster 107).
Financial support: Trans–National Institutes of Health/Food and Drug Administration (biodefense program grant).
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(See the editorial commentary by Artenstein, on pages 471–3.)







