Inter-α inhibitor proteins: a novel therapeutic strategy for experimental anthrax infection

Abstract

Human inter-α inhibitor proteins are endogenous human plasma proteins that function as serine protease inhibitors. Inter-α inhibitor proteins can block the systemic release of proteases in sepsis and block furin-mediated assembly of protective antigen, an essential stop in the intracellular delivery of the anthrax exotoxins, lethal toxin and edema toxin. Inter-α inhibitor proteins administered on hour or up to 24 h after spore challenge with Bacillus anthracis Sterne strain protected mice from lethality if administered with antimicrobial therapy (P < 0.001). These human plasma proteins possess combined actions against anthrax as general inhibitors of excess serine proteases in sepsis and specific inhibitors of anthrax toxin assembly. Inter-α inhibitor proteins could represent a novel adjuvant therapy for the treatment of established anthrax infection.

Figure 1

The lethal dose₅₀ of B. anthracis Sterne strain 34F2 after intraperitoneal administration in AJ mice. Moxi –moxifloxacin; IαIp –inter-alpha inhibitor proteins. IαIp + moxifloxacin significantly increased the LD₅₀ compared to the PBS control group. *p<0.01 **p<0.001

Figure 2

Kaplan-Meier survival plot of A/J mice exposed to 10⁶ B. anthracis Sterne strain spores at time 0. Top line - IαIp at 1 hour + moxifloxacin (10mg/kg) im q24 hrX3 (n=39). Second line - IαIp given at 24 hours plus moxifloxacin (n=27). Third line is IαIp + PBS (n=20). The fourth line is PBS + moxifloxacin (n=10); the bottom line is PBS control (n=9). The combination therapy of IαIp + moxifloxacin significantly improved the outcome compared to the placebo group (P<.001).

Figure 3

Representative Hematoxylin & Eosin stains lung tissue from animals euthanized 48 hours after the challenge with B. anthracis spores. Panel A –Lung tissue (200X- control group) showing alveolar capillaries and venules clogged with vegetative forms of B. anthracis (arrows point to bacilli in blood vessels); Panel B –Oil immersion view of an alveolar capillary with dense population of intravascular bacteria; Panel C –Tissue gram stain lung tissue (200X) from the control group showing alveolar capillaries with gram-positive bacilli and RBCs. Panel D –lung tissue (200X) in the IαIp + moxifloxacin group showing intact air spaces with minimal cellular infiltrates within the alveolar capillary membranes and the absence of bacterial invasion.

Figure 3

Representative Hematoxylin & Eosin stains lung tissue from animals euthanized 48 hours after the challenge with B. anthracis spores. Panel A –Lung tissue (200X- control group) showing alveolar capillaries and venules clogged with vegetative forms of B. anthracis (arrows point to bacilli in blood vessels); Panel B –Oil immersion view of an alveolar capillary with dense population of intravascular bacteria; Panel C –Tissue gram stain lung tissue (200X) from the control group showing alveolar capillaries with gram-positive bacilli and RBCs. Panel D –lung tissue (200X) in the IαIp + moxifloxacin group showing intact air spaces with minimal cellular infiltrates within the alveolar capillary membranes and the absence of bacterial invasion.

Figure 3

Representative Hematoxylin & Eosin stains lung tissue from animals euthanized 48 hours after the challenge with B. anthracis spores. Panel A –Lung tissue (200X- control group) showing alveolar capillaries and venules clogged with vegetative forms of B. anthracis (arrows point to bacilli in blood vessels); Panel B –Oil immersion view of an alveolar capillary with dense population of intravascular bacteria; Panel C –Tissue gram stain lung tissue (200X) from the control group showing alveolar capillaries with gram-positive bacilli and RBCs. Panel D –lung tissue (200X) in the IαIp + moxifloxacin group showing intact air spaces with minimal cellular infiltrates within the alveolar capillary membranes and the absence of bacterial invasion.

Figure 3

Representative Hematoxylin & Eosin stains lung tissue from animals euthanized 48 hours after the challenge with B. anthracis spores. Panel A –Lung tissue (200X- control group) showing alveolar capillaries and venules clogged with vegetative forms of B. anthracis (arrows point to bacilli in blood vessels); Panel B –Oil immersion view of an alveolar capillary with dense population of intravascular bacteria; Panel C –Tissue gram stain lung tissue (200X) from the control group showing alveolar capillaries with gram-positive bacilli and RBCs. Panel D –lung tissue (200X) in the IαIp + moxifloxacin group showing intact air spaces with minimal cellular infiltrates within the alveolar capillary membranes and the absence of bacterial invasion.