Proteolytic activity and fatal gram-negative sepsis in burned mice: effect of exogenous proteinase inhibition

Antibiotic-induced endotoxin release is organism-dependent in experimental Gram-negative sepsis

The majority of in vitro and animal experiments that have been performed to assess antibiotic-induced endotoxin release (AIER) have employed a single test isolate, usually Escherichia coli. To determine the influence of microorganism type on AIER and interleukin-6 (IL-6) response, CF-1 mice were made septic following a 12-15% total body surface area nonlethal burn and subeschar challenge (LD90) with Klebsiella pneumoniae K2 (∼103 cfu), Proteus mirabilis 4552 (∼101 cfu) and Pseudomonas aeruginosa SBI-N (∼102 cfu). Three intraperitoneal (i.p.) doses, given every 4 h, of ceftazidime (TAZ, 200 mg/kg), imipenem (IMI, 100 mg/kg), ciprofloxacin (CIP, 25 mg/kg) and gentamicin (GEN, 25 mg/kg) were administered post burn and infection beginning when mice were septic with organ dysfunction. Free endotoxin concentrations were significantly ( P < 0.001) higher following all antibiotics for treatment of K. pneumoniae as compared to Ps. aeruginosa (intermediate) and P. mirabilis infections. Differential AIER was highest for TAZ and IMI, intermediate for CIP and lowest for GEN, for the treatment of K. pneumoniae and Ps. aeruginosa infections. There was a strong positive correlation between endotoxin release and IL-6 production for K. pneumoniae-treated animals, however increased endotoxin levels for Pseudomonas were accompanied by decreases in IL-6 levels. For P. mirabilis infection endotoxin levels were comparatively low, but highest for GEN and IMI. However, corresponding IL-6 levels increased only 3.2-fold for IMI and actually decreased by 50% for GEN following the first dose. Interestingly, CIP resulted in only modest endotoxin release and TAZ caused no appreciable release, however IL-6 concentrations dramatically increased 39.9-fold (TAZ) and 32.6-fold (CIP). This suggests that other pro-inflammatory mediators released from the bacterium, and not endotoxin, were more important determinants in the overall host response to antibiotic exposure. In conclusion, these data provide supportive evidence that absolute and differential AIER and production of IL-6 is organism-dependent in experimental Gram-negative sepsis. As a result, general conclusions concerning differential AIER for infection caused by E. coli or K. pneumoniae cannot necessarily be extrapolated to other species of Gram-negative bacilli. Furthermore, these study results strongly indicate that the microorganism and other pertinent pro-inflammatory factors (i.e. exotoxins, proteases), must be taken into account in the study design and data analysis of any experimental or clinical trial that is conducted to determine the significance of differential AIER.

A murine model with aspects of clinical relevance for the study of antibiotic-induced endotoxin release in septic hosts

A murine model which utilizes a burn to increase susceptibility to sepsis is presented. The model is inexpensive, highly reproducible, versatile, easy to use, and clinically relevant to many aspects of a Gram-negative sepsis which develops over time from a localized focus of infection. Additionally, studies of LPS-intoxication in mice with the same burn indicate that the animals show increased sensitivity to endotoxin without having to be exposed to exogenous sensitizing chemicals. Hence, this burned mouse model of sepsis might provide a sensitive, clinically relevant model for the study of antibiotic-induced endotoxin release from Gram-negative bacteria in septic hosts.

Influence of drug class and dose size on antibiotic-induced endotoxin/IL-6 release and impact on efficacy of anti-endotoxin antibody

There are limited comparative data on antibiotic-mediated endotoxin release and cytokine liberation in septic hosts. To determine the effect of antimicrobial drug class and dose size on the relative concentration kinetics of free endotoxin and interleukin-6 (IL-6), CF-1 mice were made septic following a thermal injury and low-dose (103 CFU) subeschar challenge with Klebsiella pneumoniae serotype K2. Single intraperitoneal (i.p.) doses (in mg/kg) of ceftazidime (TAZ, 25, 200), aztreonam (AZT, 200), piperacillin (PIP, 200), meropenem (MER, 200), imipenem (IMI, 25, 100, 200), ciprofloxacin (CIP, 25) and gentamicin (GEN, 25) were administered at 72 h post burn and infection, when mice were septic with organ dysfunction. AZT, TAZ, MER, PIP (each at 200 mg/kg) and IMI (100 mg/kg) resulted in fold-increases in median endotoxin levels of 15.3, 14.9, 13.1, 8.2 and 12.4, respectively. All were significantly greater than predose baseline values (P < 0.01), however differences among agents did not reach statistical significance. The increases in free endotoxin levels for all of the beta lactams (8.2-15.3-fold) and CIP (7.7-fold) were significantly greater than for GEN (3.9-fold, P < 0.01). The fold-rise in median IL-6 concentrations from baseline for the beta lactams ranged from 3.0-7.7. All of the beta lactams resulted in statistically greater IL-6 release as compared with CIP (1.9-fold, P < 0.01) and GEN (1.4-fold, P < 0.01). The median endotoxin concentrations were significantly higher for the 100 mg/kg (668 EU/ml) and 200 mg/kg (862 EU/ml) doses of IMI compared to the 25 mg/kg dose (378 EU/mL, P < 0.05). There was also a significant increase in endotoxin levels with a dose increase of TAZ from 25 to 200 mg/kg (597 vs 1030 EU/ml, P= 0.017). The addition of antiendotoxin monoclonal antibody (E5, 2 mg/kg i.p. four times daily [qid]) to AZT (75 mg/kg qid) or TAZ (10 mg/kg qid) for 2 days significantly reduced the mortality by ∼20-40% for a 2-3 day period (P < 0.05) compared to AZT or TAZ alone. In contrast, the administration of E5 with either CIP (10 mg/kg) or GEN (10 mg/kg) by the same qid dosing schedule did not improve survival (P> 0.05). In conclusion, data from the present study, generated in a physiologically relevant model of sepsis, found relatively greater release of unbound endotoxin and IL-6 with the beta lactams, intermediate for CIP and lowest for GEN. The size of the dose of two beta lactams was also found to be a potentially important variable, suggesting that dose optimization might be possible to minimize antibiotic-associated endotoxin release. Furthermore, under our experimental conditions, the efficacy of E5 appears to be dependent upon the antibiotic with which it is administered. In order to understand better the potential significance of antibiotic-induced endotoxin release, the pharmacologic variables of the antimicrobial should be systematically evaluated in preclinical and clinical trials.

A murine model for studying endotoxemia and the efficacy of anti-LPS agents in an immunocompromised host

In most murine models of endotoxemia, an exogenous agent is injected to increase the sensitivity of the mouse to endotoxin (lipopolysaccharide, LPS). Here, a clinically encountered event, a bum, was found to reproducibly decrease the amount of LPS required to kill half of the mice (LD50). In this more clinically relevant model, the anti-LPS agents, monophosphoryl lipid A and polymyxin B sulfate, each increased the LD50 of burned mice challenged with LPS from Klebsiella pneumoniae, while the LPS-directed monoclonal antibody E5 did not. However, E5 did protect burned mice challenged with smooth or rough LPS from Salmonella typhimurium and S. minnesota, respectively. Hence, in vivo protection was dependent upon both the anti-LPS agent and the chemical composition of the LPS used for intoxication. The differences in protection observed in this intoxication model may explain some protection discrepancies reported when these anti-LPS agents have been tested for protection against Gram negative sepsis.

Disparities in efficacies of anti-LPS agents in burned mouse models of LPS intoxication versus Gram-negative sepsis

Results of anti-LPS treatments in LPS-intoxicated animals have been promising, but use of anti-LPS agents in clinical trials of sepsis have been disappointing. The purpose of this study was to determine if treatment results in intoxicated animals would hold in animal models of sepsis. Burned (15% body surface) mice were injected immediately postburn with either LPS (= intoxication) or with bacteria, which lead to sepsis. When possible, bacteria used were of the same genus and species as bacteria from which LPS was extracted for intoxication studies. Polymyxin, monophosphoryl lipid A or monoclonal antibody E5 given 1 h postburn, each protected long term against death from endotoxin intoxication. However, in septic mice, monophosphoryl lipid A and monoclonal antibody E5 did not improve survival, and polymyxin showed only transient improvement. Hence, animal models of LPS intoxication may not be optimal for testing anti-sepsis agents; use of such models, rather than of models of sepsis, may account partly for the overly optimistic expectations for anti-sepsis agents which have recently been shown to be rather ineffective in clinical trials.

Efficacy and safety profile of the novel antimicrobial peptide PXL150 in a mouse model of infected burn wounds

The urgent need to develop novel antimicrobial therapies has stimulated interest in antimicrobial peptides as therapeutic candidates for the treatment of infectious diseases. The aim of this study was to evaluate the anti-infectious effect of the synthetic antimicrobial peptide PXL150, formulated in hydroxypropyl cellulose (HPC) gel, on Pseudomonas aeruginosa in vitro and in an in vivo mouse model of infected burn wounds as well as to assess the in vivo safety profile of PXL150 in rats and rabbits. Minimal microbicidal concentration analysis showed prominent efficacy of PXL150 against P. aeruginosa in vitro, which was further enhanced in formulating the peptide in HPC gel. Application of 1.25, 2.5, 5, 10 and 20mg/g PXL150 in HPC gel twice daily for four consecutive days significantly reduced bacterial counts in the burn wounds compared with non-treated or placebo-treated controls. Continuous bioluminescence measurements of the bacteria revealed a pronounced anti-infective effect already at the first day post infection by PXL150 in concentrations of ≥2.5mg/g. In the non-clinical safety studies, PXL150 showed a favourable safety profile following repeated administration systemically and locally in rats and rabbits, respectively. In conclusion, these data support that PXL150 has the potential to be an effective and safe drug candidate for the treatment of infected burn wounds. The findings encourage the progression of PXL150 as a novel topical treatment of microbial infections.

Chitosan acetate bandage as a topical antimicrobial dressing for infected burns

An engineered chitosan acetate bandage preparation (HemCon) is used as a hemostatic dressing, and its chemical structure suggests that it should also be antimicrobial. We previously showed that when a chitosan acetate bandage was applied to full-thickness excisional wounds in mice that had been infected with pathogenic bioluminescent bacteria (Pseudomonas aeruginosa, Proteus mirabilis, and Staphylococcus aureus), it was able to rapidly kill the bacteria and save the mice from developing fatal infections. Wound healing was also stimulated. In the present study, we asked whether a chitosan acetate bandage could act as a topical antimicrobial dressing when it was applied to third-degree burns in mice contaminated with two of these bacterial species (P. aeruginosa and P. mirabilis). Preliminary experiments established the length of burn time and the number of bacteria needed to produce fatal infections in untreated mice and established that the chitosan acetate bandage could adhere to the infected burn for up to 21 days. In the case of P. aeruginosa infections, the survival rate of mice treated with the chitosan acetate bandage was 73.3% (whereas the survival rate of mice treated with a nanocrystalline silver dressing was 27.3% [P = 0.0055] and that of untreated mice was 13.3% [P < 0.0002]). For P. mirabilis infections, the comparable survival rates were 66.7%, 62.5%, and 23.1% respectively. Quantitative bioluminescent signals showed that the chitosan acetate bandage effectively controlled the growth of bacteria in the burn and prevented the development of systemic sepsis, as shown by blood culture. These data suggest that chitosan acetate bandage is efficacious in preventing fatal burn infections.

Isolation and Characterization of the ALP1 Protease from Aspergillus fumigatus and Its Protein Inhibitor from Physarium polycephalum

It is known that Aspergillus fumigatus secretes a serine protease ALP1 of the subtilisin family in the presence of extracellular protein substrates. We found conditions of A. fumigatus culturing that provide a high ALP1 activity inside cells without induction by extracellular proteins. The identity of the properties of the secreted and intracellular enzymes was shown. A thermostable protein inhibitor of the ALP1 protease was isolated from the plasmodium of the myxomycete Physarum polycephalum. Its molecular mass is 32-33 kDa. The inhibitor inhibits the ALP1 protease activity with IC50 of 0.14 microM. This protein was also shown to be a less efficient inhibitor of the activity of HIV-1 protease (IC50 2.5 microM). The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 3; see also http://www.maik.ru.

Virulence of Pseudomonas aeruginosa Cells Surviving Photodynamic Treatment with Toluidine Blue

We report results of a study carried out to investigate photodynamic effect of Touildine blue (TBO) on virulent factors secreted by Pseudomonas aeruginosa. Viability of MCF-7 cells incubated with culture supernatants of bacteria photosensitized with TBO (experimental) was found to be higher than that for MCF-7 cells incubated with culture supernatants of bacterial cells treated either with TBO in dark (control II) or not receiving any treatment (neither TBO nor light (control I)). Furthermore, whereas MCF-7 cells incubated with supernatants of bacteria, control I and II, showed significant morphological alterations, no such changes were observed in MCF-7 cells incubated with supernatant of experimental cells. The activities of phospholipase C and proteases, virulent factors of P. aeruginosa, were also found to decrease on photosensitization. These results suggest that the potency of virulent factors is reduced in cells surviving photodynamic treatment with TBO and this may have implication in treatment of infections caused by P. aeruginosa.

Locally delivered antibodies combined with systemic antibiotics confer synergistic protection against antibiotic-resistant burn wound infection

BACKGROUND

Nosocomially derived gram-negative infections, particularly from antibiotic-resistant pathogens, are a cause of morbidity in patients with severe burn wounds.

METHODS

Locally delivered polyclonal antibodies and systemically infused ceftazidime were combined in a lethal murine burn wound model against a virulent Pseudomonas aeruginosa strain that exhibits intermediate resistance to ceftazidime.

RESULTS

Survival was synergistically enhanced in cohorts of burned mice treated both locally (subeschar) with pooled polyclonal human immunoglobulin G (1-mg dose) and intravenously with infused ceftazidime (0.44 mg dose). Enhancement of survival correlated with reduced bacterial quantitation in local and systemic tissue observed in separate burned cohorts. Burned, infected mice treated prophylactically with either individual treatment at the same dose or a combination of both treatments administered systemically showed no survival enhancement as compared with the untreated control group.

CONCLUSION

Treatment of antibiotic-resistant burn wound infections with antibiotics together with locally delivered immunoglobulins may improve antibiotic protective effects against antibiotic-resistant pathogens.

The effect of photodynamic action on two virulence factors of gram-negative bacteria

Photodynamic therapy could provide an alternative to antibiotics for the treatment of local infections since a wide range of microorganisms have been shown to be susceptible to killing by photodynamic action (PDA) in vitro. The purpose of this study was to determine whether PDA was also able to affect the potency of two key bacterial virulence factors--lipopolysaccharide (LPS) and proteases. Suspensions of LPS from Escherichia coli and culture supernatants containing proteases of Pseudomonas aeruginosa were exposed to red light in the presence of toluidine blue O (TBO). The activity of each virulence factor was determined before and after irradiation. The limulus amoebocyte lysate (LAL) assay and the induction of proinflammatory cytokine (interleukin-8 and -6) release from human peripheral blood mononuclear cells (PBMC) were used for assessing the biological activity of LPS. Protease activity was quantified by azocasein hydrolysis. The biological activities of the LPS (both the LAL activity and its ability to induce cytokine release from PBMC) and the proteases were reduced significantly by irradiation with red light in the presence of TBO in a dose-dependent manner with respect to both the light energy dose and the TBO concentration. The ability of TBO-mediated PDA to reduce the activities of key virulence factors may be an additional benefit of using light-activated antimicrobial agents in the treatment of infectious diseases.

Efficacy of locally delivered polyclonal immunoglobulin against Pseudomonas aeruginosa infection in a murine burn wound model

The leading cause of morbidity and mortality in severe burn wound patients is infection. Treatment of burn wound infection is complicated by the emergence of antibiotic resistant organisms. A potential therapeutic alternative to antibiotic drugs is the local administration of polyclonal antibodies, termed passive local immunotherapy (PLI), directly to the burned tissue. A mouse burn wound infection model to simulate full thickness burn wound infection was used to evaluate the efficacy of passive local immunotherapy as a viable prophylactic or therapeutic agent. Pooled human immunoglobulins (IgG), delivered locally to the site of infection, are shown to be more effective at preventing fatal burn wound sepsis than treatment by intravenous infusion of IgG. A single 10 mg dose of human IgG administered locally to the burned, infected tissue site, either 24 hours prior to bacterial challenge, or within 3 hours after bacterial challenge, enhanced animal survival significantly (P < 0.001 and P < 0.05 respectively) compared to control animals. In addition, reduced levels of bacteria were found in local and systemic tissues of IgG-treated mice compared to control mice (P < 0.05). These data support the local use of polyclonal immunoglobulin preparations as an efficacious and cost effective means to prevent and treat burn wound infections.

High-dose antithrombin III treatment of severely injured patients: results of a prospective study

BACKGROUND

Antithrombin III (AT III) treatment has been shown to reduce disseminated intravascular coagulation and to inhibit thrombin, which plays a central role in the activation of platelets and other inflammatory systems in conditions with severe inflammation. The objective of this study was to evaluate the influence of early and high-dose administration of AT III to patients with severe multiple injuries on the inflammatory response and outcome.

METHODS

In a placebo-controlled, double-blind study, 40 consecutive patients with Injury Severity Scores of 29 or greater who met the inclusion criteria were randomized to receive either AT III or placebo within 360 minutes after trauma. Twenty patients were administered AT III for a period of 4 days, aiming to achieve AT III concentrations of 140% of normal.

RESULTS

The AT III and placebo groups were comparable with respect to Injury Severity Score, age, incidence of blood pressure less than 80 mm Hg on admission, initial base deficit, and start of the test drug. The patients in the AT III group received a total of about 20,000 IU during the first 4 days. AT III levels of 130 to 140% could be achieved by this regimen, whereas in the control group the AT III concentration averaged about 70%. In the AT III group prothrombin tended to be elevated and prothrombin fragment F1+2 as well as thrombin-AT III complex tended to be lower on the first day. No differences between groups, however, could be observed with respect to partial thromboplastin time, prothrombin time, platelets, plasminogen activator inhibitor I, soluble tumor necrosis factor receptor II, neutrophil elastase, interleukin (IL)-1 receptor antagonist, IL-6, and IL-8. Mortality (15 vs. 5%), incidence of respiratory failure (55 vs. 55%), duration of mechanical ventilation (13 vs. 12 days), and length of stay in the surgical intensive care unit (19 vs. 21 days) were also similar in both treatment groups. The duration of organ failure, however, was shorter in the patients receiving AT III.

CONCLUSION

The early and high-dose administration of AT III to patients with severe blunt trauma appears not to attenuate the posttraumatic inflammatory response or to significantly improve outcome.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Effect of thermal injury on the adherence of Candida albicans to murine splenic tissue

In a mouse model of thermal injury, an increase in burn size produced a decrease in the ratio of Candida albicans cells adherent to the marginal zone to those adherent to the white pulp of the spleen, an increase in the number of Candida cells in the circulation and in the kidneys, and an increase in mortality.

Circulating levels of tumour necrosis factor, interleukin 6 and proteolytic activity in a murine model of burn and infection

Cytokines and proteinases have both been implicated as mediators in the inflammatory response associated with trauma and sepsis. Using a burned-infected mouse model, it was previously found that mortality is proportional to the amount of proteolytic activity (PA) in the circulation. However, little is known about circulating cytokine levels in hosts that are both burned and infected. With this mouse model, both tumour necrosis factor (TNF) and interleukin 6 (IL-6) were upregulated by a burn and by an infection. Burn plus infection produced an additive effect on each cytokine, but IL-6 levels correlated better with mortality. Treating mice with the proteinase inhibitor aprotinin immediately preburn and infectious challenge significantly decreased IL-6, PA and mortality. This may be a clinically relevant model for studying mediators in burned and/or septic hosts.