In vivo interaction of endotoxin and recombinant bactericidal/permeability-increasing protein (rBPI23): hemodynamic effects in a human endotoxemia model

Review: From therapy to experimental model: a hundred years of endotoxin administration to human subjects

This article is a review of studies in which endotoxin has been administered to human subjects for experimental purposes. Data are presented in tabular form so the reader can better appreciate the objectives of individual studies. Although the original intention was to focus on the adverse events associated with these studies, unexpected serious adverse events rarely have been reported.

Sepsis in standard care: patients' characteristics, effectiveness of antimicrobial therapy and patient outcome--a cohort study

PURPOSE

Fast diagnosis and initiation of appropriate antibiotic therapy is pivotal for the survival of sepsis patients. However, most studies on suspected sepsis patients are conducted in the intensive care unit or in the emergency room setting, neglecting the standard care setting. This study evaluated sepsis risk factors, microbiological accurateness of the initial empiric antimicrobial therapy and its effect on hospital mortality in standard care patients.

METHODS

In this prospective observational cohort study, patients with clinically suspected sepsis meeting two or more SIRS criteria were screened on standard care wards. After hospital discharge, occurrence of an infection was assessed according to standardized criteria, and empirical antibiotic therapy was evaluated using antibiograms of recognized pathogens by expert review.

RESULTS

Of the 2384 screened patients, 298 fulfilled two or more SIRS criteria. Among these were 28.2 % SIRS patients without infection, 46.3 % non-bacteremic/fungemic sepsis patients and 25.5 % bacteremic/fungemic sepsis patients. Occurrence of a malignant disease and chills were associated with a higher risk of patients having bacteremic/fungemic sepsis, whereas other described risk factors remained insignificant. In total, 91.1 % of suspected sepsis patients received empirical antimicrobial therapy, but 41.1 % of bacteremic sepsis patients received inappropriate therapy. Non-surviving bacteremic sepsis patients received a higher proportion of inappropriate therapy than those who survived (p = 0.022).

CONCLUSIONS

A significant proportion of bacteremic sepsis patients receive inappropriate empiric antimicrobial therapy. Our results indicate that rapid availability of microbiological results is vital, since inappropriate antimicrobial therapy tended to increase the hospital mortality of sepsis patients.

Low dose LPS does not increase TLR4 expression on monocytes in a human in vivo model

BACKGROUND AND PURPOSE

Toll like receptor 4 (TLR4) is the major recognition receptor for lipopolysaccharides and plays a major role in the inflammatory response. CD11b is expressed on the surface of many leukocytes including monocytes. The CD11b/CD18 complex is involved in the inflammatory response by mediating migration and adhesion of leukocytes. The aim of this human in vivo study was to investigate the expression of TLR4 and CD11b on the surface of human monocytes after in vivo low-dose LPS stimulation.

METHODS

We performed a double-blind, randomized crossover study with 16 healthy males who received a bolus injection of bacterial lipopolysaccharide (LPS; 0.4ng/kg) or normal saline. Vital parameters, blood counts, serum cytokine levels, the expression of TLR4, and CD11b on CD14 positive cells were analyzed.

RESULTS

The experimentally induced inflammatory response was reflected by transient increases in body temperature, circulating leukocyte numbers, and plasma levels of pro- (TNF-α, IL-6) and anti-inflammatory cytokines (IL-10, IL-1ra). In contrast to a significant increase in CD11b expression, no changes in TLR4 expression on circulating monocytes were detectable.

CONCLUSION

Early changes in TLR4 expression on circulating monocytes are not necessarily part of the inflammatory response to low dose LPS in humans whereas the detected increase of CD11b expression might already be sufficient for optimized recognition and signalling.

Endotoxemia reduces cerebral perfusion but enhances dynamic cerebrovascular autoregulation at reduced arterial carbon dioxide tension

OBJECTIVE

The administration of endotoxin to healthy humans reduces cerebral blood flow but its influence on dynamic cerebral autoregulation remains unknown. We considered that a reduction in arterial carbon dioxide tension would attenuate cerebral perfusion and improve dynamic cerebral autoregulation in healthy subjects exposed to endotoxemia.

DESIGN

Prospective descriptive study.

SETTING

Hospital research laboratory.

SUBJECTS

Ten healthy young subjects (age: 32 ± 8 yrs [mean ± SD]; weight: 84 ± 10 kg; weight: 184 ± 5 cm; body mass index: 25 ± 2 kg/m2) participated in the study.

INTERVENTIONS

Systemic hemodynamics, middle cerebral artery mean flow velocity, and dynamic cerebral autoregulation evaluated by transfer function analysis in the very low (<0.07 Hz), low (0.07-0.15 Hz), and high (>0.15 Hz) frequency ranges were monitored in these volunteers before and after an endotoxin bolus (2 ng/kg; Escherichia coli).

MEASUREMENTS AND MAIN RESULTS

Endotoxin increased body temperature of the subjects from 36.8 ± 0.4°C to 38.6 ± 0.5°C (p < .001) and plasma tumor necrosis factor-α from 5.6 (2.8-6.7) pg/mL to 392 (128-2258) pg/mL (p < .02). Endotoxemia had no influence on mean arterial pressure (95 [74-103] mm Hg vs. 92 [78-104] mm Hg; p = .75), but increased cardiac output (8.3 [6.1-9.5] L·min(-1) vs. 6.0 [4.5-8.2] L·min(-1); p = .02) through an elevation in heart rate (82 ± 9 beats·min(-1) vs. 63 ± 10 beats·min(-1); p < .001), whereas arterial carbon dioxide tension (37 ± 5 mm Hg vs. 41 ± 2 mm Hg; p < .05) and middle cerebral artery mean flow velocity (37 ± 9 cm·sec(-1) vs. 47 ± 10 cm·sec(-1); p < .01) were reduced. In regard to dynamic cerebral autoregulation, endotoxemia was associated with lower middle cerebral artery mean flow velocity variability (1.0 ± 1.0 [cm·sec(-1)] Hz vs. 2.8 ± 1.5 [cm·sec(-1)] Hz; p < .001), reduced gain (0.52 ± 0.11 cm·sec(-1) x mm Hg(-1) vs. 0.74 ± 0.17 cm·sec(-1) x mm Hg(-1); p < .05), normalized gain (0.22 ± 0.05 vs. 0.40 ± 0.17%·%; p < .05), and higher mean arterial pressure-to-middle cerebral artery mean flow velocity phase difference (p < .05) in the low frequency range (0.07-0.15 Hz).

CONCLUSIONS

These data support that the reduction in arterial carbon dioxide tension explains the improved dynamic cerebral autoregulation and the reduced cerebral perfusion encountered in healthy subjects during endotoxemia.

C1-esterase inhibitor attenuates the inflammatory response during human endotoxemia

OBJECTIVE

Besides its role in regulation of the complement and contact system, C1-esterase inhibitor has other immunomodulating effects that could prove beneficial in patients with acute inflammation such as during sepsis or after trauma. We examined the immunomodulating properties of C1-esterase inhibitor during human experimental endotoxemia, in which the innate immune system is activated in the absence of activation of the classic complement pathway.

DESIGN

Double-blind placebo-controlled study.

SETTING

Research intensive care unit of the Radboud University Nijmegen Medical Centre.

SUBJECTS

Twenty healthy volunteers.

INTERVENTIONS

Intravenous injection of 2 ng/kg Escherichia coli lipopolysaccharide. Thirty minutes thereafter (to prevent binding of lipopolysaccharide), C1-esterase inhibitor concentrate (100 U/kg, n = 10) or placebo (n = 10) was infused.

MEASUREMENTS AND MAIN RESULTS

Pro- and anti-inflammatory mediators, markers of endothelial and complement activation, hemodynamics, body temperature, and symptoms were measured. C1-esterase inhibitor reduced the release of proinflammatory cytokines as well as C-reactive protein (peak levels of: interleukin-6 1521 ± 209 vs. 932 ± 174 pg/mL [p = .04], tumor necrosis factor-α 1213 ± 187 vs. 827 ± 167 pg/mL [p = .10], monocyte chemotactic protein-1 6161 ± 1302 vs. 3373 ± 228 pg/mL [p = .03], interleukin-1β 34 ± 5 vs. 23 ± 2 pg/mL [p < .01], C-reactive protein 39 ± 4 vs. 29 ± 2 mg/L [p = .02]). In contrast, release of the anti-inflammatory cytokine interleukin-10 was increased by C1-esterase inhibitor (peak level 73 ± 11 vs. 121 ± 18 pg/mL, p = .02). The increase in interleukin-1 receptor antagonist tended to be smaller in the C1-esterase inhibitor group, but this effect did not reach statistical significance (p = .07). Markers for endothelial activation were increased after lipopolysaccharide infusion, but no significant differences between groups were observed. The lipopolysaccharide-induced changes in heart rate, blood pressure, body temperature, and symptoms (all p < .001 over time) were not influenced by C1-esterase inhibitor. Complement fragment C4 was not increased after lipopolysaccharide challenge.

CONCLUSIONS

This study is the first to demonstrate that C1-esterase inhibitor exerts anti-inflammatory effects in the absence of classic complement activation in humans.

Systemic endotoxin levels in chronic indolent periodontal infections

BACKGROUND AND OBJECTIVE

Periodontal disease has been linked with an increased risk of various systemic diseases. A plausible biologic explanation for this link includes the opportunity for oral pathogens to translocate to the circulation as a result of breakdown in integrity of the oral epithelium. This study refined a methodology used to detect endotoxin activity in the serum of subjects with indolent periodontal infections.

MATERIAL AND METHODS

The QCL Kinetic Chromogenic Assay (Cambrex) is a kinetic measure of endotoxin activity. Sera from 211 pregnant women with periodontitis enrolled in the Obstetrics and Periodontal Therapy Trial were used to develop the assay further and to evaluate the detection of endotoxin activity that might accompany a low-level bacteremia in chronic periodontitis.

RESULTS

We optimized the system to increase the sensitivity and reproducibility of the assay. The refined system was able to detect endotoxin activity in serum at > 0.0125 EU/mL. At baseline (13-16 wk of gestation), 35.5% of the women were positive for endotoxin activity (1.62 +/- 2.21; range: 0.38-15 EU/mL).

CONCLUSION

This report describes a sensitive measure of endotoxin activity in serum. The procedure allowed us to document levels of this microbial virulence factor in serum of individuals with indolent infections such as periodontal disease.

Lipopolysaccharide-stimulated whole blood cytokine production does not predict the inflammatory response in human endotoxemia

A widely applied method to study the activation of the innate immune system is in vitro stimulation of whole blood using lipopolysaccharide (LPS). However, it is unclear if in vitro cytokine production relates to in vivo cytokine levels elicited during experimental endotoxemia or sepsis. To determine the correlation between in vitro cytokine production and the in vivo inflammatory response, blood was obtained from 15 healthy volunteers for in vitro incubation with Escherichia coli LPS, immediately followed by experimental E. coli endotoxemia. Correlations of in vitro and peak in vivo cytokine concentrations were determined using Pearson correlation coefficient. In stimulated whole blood, tumor necrosis factor (TNF)-α, Interleukin (IL)-1β, IL-6, IL-10 and interferon (IFN)-γ were induced to 279 ± 53, 392 ± 64, 5312 ± 624, 83 ± 20 and 343 ± 85 pg/ml, respectively, whereas in vivo cytokine induction led to cytokine levels of 603 ± 123, 11 ± 1, 4999 ± 1228, 167 ± 25 and 194 ± 40 pg/ml, respectively. Correlation coefficients between the in vitro and in vivo cytokine concentrations were for TNF-α, IL-1β, IL-6, IL-10 and IFN-γ -0.10 (P = 0.7), 0.09 (P = 0.8), 0.36 (P = 0.2), 0.19 (P = 0.5) and 0.40 (P = 0.1), respectively. Comparison between in vitro and in vivo stimulation with LPS shows no correlation between the amount of cytokines produced. In vitro cytokine production, therefore, does not predict the in vivo inflammatory response.

Sepsis strategies in development

Severe sepsis, defined as inflammation and organ failure due to infection, continues to result in a mortality of approximately 30% despite advances in critical care. Current therapy includes timely administration of antibiotics, source control of infection, aggressive fluid resuscitation, support of failing organs, and use of activated protein C where clinically indicated. Bacterial mediators, including endotoxin and superantigens, as well endogenous proinflammatory cytokines are considered important to the pathogenesis of sepsis-induced organ failure and are being targeted with numerous molecules and removal devices. Additional therapeutic strategies are aimed at restoring the natural anticoagulant levels, blocking deleterious effects of the complement cascade, reversing cytopathic hypoxia, and inhibiting excessive lymphocyte apoptosis. Molecules with pluripotent activity, such as interalpha inhibitor proteins and estrogen-receptor ligands, are also being investigated.

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

Gram-negative bacteria (GNB) and their endotoxin present a constant environmental challenge. Endotoxins can potently signal mobilization of host defenses against invading GNB but also potentially induce severe pathophysiology, necessitating controlled initiation and resolution of endotoxin-induced inflammation to maintain host integrity. The bactericidal/permeability-increasing protein (BPI) is a pluripotent protein expressed, in humans, mainly neutrophils. BPI exhibits strong antimicrobial activity against GNB and potent endotoxin-neutralizing activity. BPI mobilized with neutrophils in response to invading GNB can promote intracellular and extracellular bacterial killing, endotoxin neutralization and clearance, and delivery of GNB outer membrane antigens to dendritic cells. Tissue expression by dermal fibroblasts and epithelia could further amplify local levels of BPI and local interaction with GNB and endotoxin, helping to constrain local tissue infection and inflammation and prevent systemic infection and systemic inflammation. This review article focuses on the structural and functional properties of BPI with respect to its contribution to host defense during GNB infections and endotoxin-induced inflammation and the genesis of autoantibodies against BPI that can blunt BPI activity and potentially contribute to chronic inflammatory disease.

Bactericidal/permeability increasing protein attenuates the myocardial inflammation/dysfunction that occurs with burn complicated by subsequent infection

Intubation and mechanical ventilation after burn contribute to pneumonia-related infection. Although postburn presence or absence of endotoxin has been described, inactivation of Toll-like receptor 4 signaling has been shown to improve postburn organ function, suggesting that LPS participates in burn-related susceptibility to infection. We hypothesized that bactericidal/permeability-increasing protein (rBPI) given postburn would attenuate myocardial inflammation/dysfunction associated with postburn septic challenge given 7 days postburn. Rats were given burn over 40% total body surface area, lactated Ringer 4 ml.kg(-1).% burn(-1); burns received either vehicle or rBPI, 1 mg.kg(-1).h(-1) for 48 h postburn. Postburn day 7, subgroups of burns and shams were given intratracheal Klebsiella pneumoniae, 4 x 10(6) CFU to produce burn complicated by sepsis; additional sham and burn subgroups received intratracheal vehicle to produce sham sepsis. Vehicle-treated groups: 1) sham burn + sham sepsis 2) sham burn + sepsis, 3) burn + sham sepsis, 4) burn + sepsis. rBPI-treated groups: 5) sham burn + sham sepsis, 6) sham burn + sepsis, 7) burn + sham sepsis, 8) burn + sepsis. Cardiomyocyte cytokine secretion and myocardial function were studied 24 h after septic challenge, postburn day 8. Pneumonia-related infection 8 days after vehicle-treated burn produced myocyte cytokine secretion (pg/ml), indicated by increased myocyte TNF-alpha, 549 +/- 46; IL-1beta, 50 +/- 8; IL-6, 286 +/- 3 levels compared with levels in sham myocytes (TNF-alpha, 88 +/- 11; IL-1beta, 7 +/- 1; IL-6, 74 +/- 10; P < 0.05). Contractile dysfunction was evident from lower left ventricular pressure +/-dP/dt values in this group compared with sham. rBPI attenuated myocyte cytokine responses to septic challenge and improved contractile function, suggesting that burn-related mobilization of microbial-like products contribute to postburn susceptibility to infection.

Non-invasive pulsatile arterial pressure and stroke volume changes from the human finger

In this paper we review recent developments in the methodology of non-invasive finger arterial pressure measurement and the information about arterial flow that can be obtained from it. Continuous measurement of finger pressure based on the volume-clamp method was introduced in the early 1980s both for research purposes and for clinical medicine. Finger pressure tracks intra-arterial pressure but the pressure waves may differ systematically both in shape and magnitude. Such bias can, at least partly, be circumvented by reconstruction of brachial pressure from finger pressure by using a general inverse anti-resonance model correcting for the difference in pressure waveforms and an individual forearm cuff calibration. The Modelflow method as implemented in the Finometer computes an aortic flow waveform from peripheral arterial pressure by simulating a non-linear three-element model of the aortic input impedance. The methodology tracks fast changes in stroke volume (SV) during various experimental protocols including postural stress and exercise. If absolute values are required, calibration against a gold standard is needed. Otherwise, Modelflow-measured SV is expressed as change from control with the same precision in tracking. Beat-to-beat information on arterial flow offers important and clinically relevant information on the circulation beyond what can be detected by arterial pressure.