Anthrax lethal and edema toxins produce different patterns of cardiovascular and renal dysfunction and synergistically decrease survival in canines

Abstract

Background: High mortality in the 2001 US and recent European anthrax outbreaks suggests that better understanding of the effects of the toxins produced by this bacterium is needed to improve treatment.

Methods and results: Here, 24-h edema (ETx) and lethal (LeTx) toxin infusions were investigated for 96 hin sedated canines receiving mechanical ventilation. The initial study compared similarly lethal doses of ETx (n=8) or LeTx (n=15) alone. ETx was 24 times less lethal than LeTx, and the median time to death in nonsurvivors (n=6 and n=9, respectively) was shorter with ETx (42 vs 67 h; P=.04). Compared with controls(n=9), both toxins decreased arterial and central venous pressures and systemic vascular resistance and increased heart rate, cardiac index, blood urea nitrogen (BUN) level, creatinine (Cr) concentration, BUN:Cr ratio, and hepatic transaminase levels (P ≤ .05 for toxin effect or time interaction). However, ETx stimulated early diuresis,reduced serum sodium levels, and had more pronounced vasodilatory effects, compared with LeTx, as reflected by greater or earlier central venous pressures, systemic vascular resistance, and changes in the BUN:Cr ratio(P ≤ .01). LeTx progressively decreased the left ventricular ejection fraction (P ≤ .002). In a subsequent study, a lethal dose of LeTx with an equimolar nonlethal ETx dose (n=8) increased mortality, compared with LeTx alone (n=8; P= .05).

Conclusion: Shock with ETx or LeTx may require differing supportive therapies, whereas toxin antagonists should likely target both toxins.

Figure 1

A and B, Survival times associated with decreasing doses of edema (ETx) or lethal (LeTx) toxin in individual animals from study 1 (reported as the dose of edema or lethal factor used). Gray circles indicate doses that were associated with both survivors (survival time, 96 h) and nonsurvivors (survival time, <96 h), and black circles indicate doses for which no animal survived (termed low- and high-dose groups, respectively). C and D, Proportion of animals surviving over time with the administration of either low or high doses of ETx or LeTx or diluent only (controls) in study 1. E, Proportion of animals surviving over time in study 2, which compared LeTx and ETx alone or together with controls. Control animals (C, D, and E) represent animals investigated in both studies 1 and 2. The horizontal arrow (†) indicates the 24-h period over which toxin or control challenge was infused.

Figure 2

Mean serial effects (± standard error of the mean) in a comparison to controls (see Methods) with low (LD) and high (HD) doses of edema (ETx) and lethal (LeTx) toxin on changes from baseline in study 1, for mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP), cardiac index (CI), systemic vascular resistance index, and left ventricular ejection fraction (LVEF). The shaded area indicates the 24-h toxin infusion period. P values are shown for the overall effect of toxin compared to control (p^α) and for the interaction between time and this effect (p^β). Increases or decreases with toxin, compared with controls, are indicated by symbols above or below the dashed horizontal no-effect line, respectively. Because measurements were performed in all animals available for study at each time point, the number of measures used for analysis are shown by the number of animals surviving from each group at a particular time point in the Kaplan-Meier curves in Figure 1C and 1D. For clarity of presentation, however, the toxin effects (ie, toxin minus control) are shown.

Figure 3

Mean serial effects (± standard error of the mean) in a comparison of controls with low (LD) or high (HD) doses of edema (ETx) and lethal (LeTx) toxin on changes from baseline in study 1 for blood urea nitrogen (BUN) level, creatinine (Cr) level, BUN:Cr ratio, sodium (Na; 24-h urine output), and aspartate aminotransferase (AST) level. The format is similar to Figure 2.

Figure 4

Mean effects (± standard error of the mean) of a fluid bolus (40 mL/kg intravenously over 40 min) in study 1 for central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), mean arterial blood pressure (MAP), and cardiac index (CI) in animals receiving 24-h infusions with low (LD) or high (HD) doses of edema (ETx) or lethal (LeTx) toxin or in controls. P values are for the comparison between the effect of fluid in toxin animals versus control (p^α) and for the interaction between time and these comparisons (p^β).

Figure 5

Mean serial effects (± standard error of the mean) in a comparison of controls with a median lethal dose (LD₅₀) of lethal toxin (LeTx), an equal molar dose of edema toxin (ETx), or the combination (ETx + LeTx) on changes from baseline in study 2 for mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP), cardiac index (CI), systemic vascular resistance index, and left ventricular ejection fraction (LVEF). The format is similar to Figure 2.

Figure 6

Mean serial effects (± standard error of the mean) in a comparison of controls with a median lethal dose (LD₅₀) of lethal toxin (LeTx), an equal molar dose of edema toxin (ETx), or the combination (ETx + LeTx) on changes from baseline in study 2 for blood urea nitrogen (BUN) level, creatinine (Cr) level, BUN:Cr ratio, sodium (Na; 24-h urine output) level, and aspartate aminotransferase (AST) level. The format is similar to Figure 2.

Table 1

Summary of the Challenge Type, Dose, and Associated Survival in Individual Animals in Sequential Experiments

Table 1

Summary of the Challenge Type, Dose, and Associated Survival in Individual Animals in Sequential Experiments