New criteria for selecting the proper antimicrobial chemotherapy for severe sepsis and septic shock

Potent Anti-Inflammatory Effects of a Helix-to-Helix Peptide against Pseudomonas aeruginosa Endotoxin-Mediated Sepsis

Although considerable scientific research data is available for sepsis and cytokine storm syndrome, there is a need to develop new treatments or drugs for sepsis management. Antimicrobial peptides (AMPs) possess anti-bacterial and anti-inflammatory activity, neutralizing toxins such as lipopolysaccharides (LPS, endotoxin). Most AMPs have been designed as a substitute for conventional antibiotics, which kill drug-resistant pathogens. The present study aimed to determine the anti-inflammatory potential of 10 designed XIW (X: lysine, arginine, or glutamic acid) α-helical peptides in macrophages and a mouse model in the presence of LPS. Among them, WIKE-14, a peptide with a helix-to-helix structure, having the 12th amino acid substituted with glutamic acid, suppressed pro-inflammatory cytokines in RAW 264.7 macrophages. This reaction was mediated by the inhibition of the binding between LPS and macrophages. In addition, the WIKE-14 peptide exhibited a potent anti-inflammatory activity in mice ears and lungs inflamed using LPS. Thus, our results may provide useful insights for the development of anti-sepsis agents via the sequence and structure information of the WIKE-14 peptide.

Filamentous morphology of bacterial pathogens: regulatory factors and control strategies

Several studies have demonstrated that when exposed to physical, chemical, and biological stresses in the environment, many bacteria (Gram-positive and Gram-negative) change their morphology from a normal cell to a filamentous shape. The formation of filamentous morphology is one of the survival strategies against environmental stress and protection against phagocytosis or protist predators. Numerous pathogenic bacteria have shown filamentous morphologies when examined in vivo or in vitro. During infection, certain pathogenic bacteria adopt a filamentous shape inside the cell to avoid phagocytosis by immune cells. Filamentous morphology has also been seen in biofilms formed on biotic or abiotic surfaces by certain bacteria. As a result, in addition to protecting against phagocytosis by immune cells or predators, the filamentous shape aids in biofilm adhesion or colonization to biotic or abiotic surfaces. Furthermore, these filamentous morphologies of bacterial pathogens lead to antimicrobial drug resistance. Clinically, filamentous morphology has become one of the most serious challenges in treating bacterial infection. The current review went into great detail about the various factors involved in the change of filamentous morphology and the underlying mechanisms. In addition, the review discussed a control strategy for suppressing filamentous morphology in order to combat bacterial infections. Understanding the mechanism underlying the filamentous morphology induced by various environmental conditions will aid in drug development and lessen the virulence of bacterial pathogens. KEY POINTS: • The bacterial filamentation morphology is one of the survival mechanisms against several environmental stress conditions and protection from phagocytosis by host cells and protist predators. • The filamentous morphologies in bacterial pathogens contribute to enhanced biofilm formation, which develops resistance properties against antimicrobial drugs. • Filamentous morphology has become one of the major hurdles in treating bacterial infection, hence controlling strategies employed for inhibiting the filamentation morphology from combating bacterial infections.

Joint effect of surfactants and cephalexin on the formation of Escherichia coli filament

Both antibiotics and surfactants commonly exist in natural environment and have generated great concerns due to their biological influence on the ecosystem. A major concern lies in the capacity of antibiotics to induce bacterial filaments formation, which has potential health risks. However, their joint effect is not clear so far. Here, we studied the joint effect of cephalexin (Cex), a typical antibiotic, and differently charged surfactants on the formation of E. coli filaments. Three kinds of surfactants characterized by different charges were used: cationic surfactant (CTAB), anionic surfactant (SDS) and nonionic surfactant (Tween). Data showed that Cex alone caused the formation of E. coli filaments, elongating their maximum profile from ca. 2 μm (a single E. coli cell) to tens of micrometers (an E. coli filament). A joint use of surfactants with Cex could produce even longer E. coli filaments, elongating the maximum length of the bacteria to larger than 100 μm. The capacity order of different surfactants under their optimum concentrations to produce elongated E. coli filaments was Tween > SDS > CTAB. The E. coli filaments were characterized with a normal DNA distribution and a good cell membrane integrity. We measured the stiffness of bacterial cell wall by atomic force microscopy and correlated the elongation capacity of the E. coli filaments to the stiffness of cell wall. Zeta potential measurement indicated that inserting into or being bound to the cell surface in a large quantity was tested not to be the major way that surfactants interacted with bacteria.

Anti-endotoxin properties of cationic host defence peptides and proteins

The innate immune system of mammals contains a series of peptides with overall positive charge and an amphipathic structure which have a variety of important properties in host defences. Although these are often termed cationic antimicrobial peptides, they have numerous roles in innate defences in all complex species of life and thus we prefer to refer to them as host defence peptides. These roles include: (i) an ability to kill micro-organisms directly, ranging from bacteria to viruses, fungi, parasites and helminths; (ii) an adjuvant activity in the adaptive response; and (iii) a multiplicity of roles in modulating innate immunity, including an apparent ability to stimulate protective innate immunity while suppressing harmful inflammatory/septic responses. This latter property may be one of the more important activities of these peptides in vivo. Innate immunity is thought to be triggered by the interaction of conserved bacterial components with particular receptors including Toll-like receptors (TLRs) on host cells. However, the initiation of the innate immune response through this route may trigger a pro-inflammatory cascade that is the principle cause of harmful conditions such as sepsis. Since we are exposed to potentially dangerous pathogens on a daily basis, the host response must contain certain checks and balances. We propose that host defence peptides have a role in feed-back modulation of inflammation under normal (low-pathogen exposure) conditions. This review surveys the available information regarding the antiendotoxic/anti-inflammatory properties of host defence peptides, and will address whether this potential might be exploited for therapeutic benefit in sepsis.

Automated image analysis for quantification of filamentous bacteria

Background

Antibiotics of the β-lactam group are able to alter the shape of the bacterial cell wall, e.g. filamentation or a spheroplast formation. Early determination of antimicrobial susceptibility may be complicated by filamentation of bacteria as this can be falsely interpreted as growth in systems relying on colorimetry or turbidometry (such as Vitek-2, Phoenix, MicroScan WalkAway). The objective was to examine an automated image analysis algorithm for quantification of filamentous bacteria using the 3D digital microscopy imaging system, oCelloScope.

Results

Three E. coli strains displaying different resistant profiles and differences in filamentation kinetics were used to study a novel image analysis algorithm to quantify length of bacteria and bacterial filamentation. A total of 12 β-lactam antibiotics or β-lactam–β-lactamase inhibitor combinations were analyzed for their ability to induce filamentation. Filamentation peaked at approximately 120 min with an average cell length of 30 μm.

Conclusion

The automated image analysis algorithm showed a clear ability to rapidly detect and quantify β-lactam-induced filamentation in E. coli. This rapid determination of β-lactam-mediated morphological alterations may facilitate future development of fast and accurate AST systems, which in turn will enable early targeted antimicrobial therapy. Therefore, rapid detection of β-lactam-mediated morphological changes may have important clinical implications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0583-5) contains supplementary material, which is available to authorized users.

Esculentin(1-21), an amphibian skin membrane-active peptide with potent activity on both planktonic and biofilm cells of the bacterial pathogen Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that forms sessile communities, named biofilms. The non-motile forms are very difficult to eradicate and are often associated with the establishment of persistent infections, especially in patients with cystic fibrosis. The resistance of P. aeruginosa to conventional antibiotics has become a growing health concern worldwide and has prompted the search for new anti-infective agents with new modes of action. Naturally occurring antimicrobial peptides (AMPs) represent promising future template candidates. Here we report on the potent activity and membrane-perturbing effects of the amphibian AMP esculentin(1-21), on both the free-living and sessile forms of P. aeruginosa, as a possible mechanism for biofilm disruption. Furthermore, the findings that esculentin(1-21) is able to prolong survival of animals in models of sepsis and pulmonary infection indicate that this peptide can be a promising template for the generation of new antibiotic formulations to advance care of infections caused by P. aeruginosa.

Esculentin 1-21: a linear antimicrobial peptide from frog skin with inhibitory effect on bovine mastitis-causing bacteria

Mastitis, or inflammation of the mammary gland, is the most common and expensive illness of dairy cows throughout the world. Although stress and physical injuries may give rise to inflammation of the udders, infections by bacteria or other microorganisms remain the major cause, and infusion of antibiotics is the main treatment approach. However, the increased emergence of multidrug-resistant pathogens and the production of milk contaminated with antibiotics has become a serious threat in the livestock. Hence, there is an urgent need for the discovery of new therapeutic agents with a new mode of action. Gene-encoded AMPs, which represent the first line of defence in all living organisms, are considered as promising candidates for the development of new anti-infective agents. This paper reports on the antibacterial activities in vitro and in an animal model, of the frog skin AMP esculentin 1-21 [Esc(1-21)], along with a plausible mode of action. Our data revealed that this peptide (i) is highly potent against the most common mastitis-causing microbes (e.g. Streptococcus agalactiae); and (ii) is active in vivo, causing a visible regression of the clinical stage of mastitis in dairy cows, after 1 week of peptide treatment. Biophysical characterisation revealed that the peptide adopts an alpha-helical structure in microbial mimicking membranes and is able to permeate the membrane of S. agalactiae in a dose-dependent manner. Overall, these data suggest Esc(1-21) as an attractive AMP for the future design of new antibiotics to cure mastitis in cattle.

Alexidine and chlorhexidine bind to lipopolysaccharide and lipoteichoic acid and prevent cell activation by antibiotics

OBJECTIVES

Many antibiotics used to treat infections cause release of immunostimulatory cell wall components from bacteria. Therefore, a combination of antimicrobial and endotoxin-neutralizing activity is desired to prevent inflammation induced by destroyed bacteria. Chlorhexidine and alexidine are amphipathic bisbiguanides and could neutralize bacterial membrane components as stimulators of Toll-like receptors (TLRs).

METHODS

Binding of chlorhexidine and alexidine to lipopolysaccharide (LPS) and lipoteichoic acid (LTA) was determined by fluorescence displacement assay and isothermal calorimetric titration. Neutralization of the biological effect of LPS and LTA on TLR-activated cellular activation was determined by NF-kappaB reporter luciferase activation on cells transfected with specific TLRs and NO production of murine macrophages in the presence of isolated agonists and antibiotic-treated bacteria.

RESULTS

Alexidine and chlorhexidine bind not only to LPS but also to LTA from Gram-positive bacteria. Alexidine has a higher affinity than chlorhexidine for both compounds. Calorimetric titration shows an initial endothermic contribution indicating participation of hydrophobic interactions in LPS binding, while binding to LTA displayed initial exothermic contribution. Both compounds prevent cell activation of TLR4 and TLR2 by LPS and LTA, respectively. The addition of both compounds suppressed NO production by macrophages in the presence of bacteria treated with different types of antibiotics.

CONCLUSIONS

Chlorhexidine and alexidine suppress bacterial membrane-induced cell activation at concentrations two orders of magnitude lower than that used in topical applications. Combining biocides with different types of antibiotics prevented macrophage activation in the presence of bacteria and demonstrated the potential of chlorhexidine and alexidine to suppress inflammatory responses caused by activation of TLRs.

Impact of carbapenem administration on systemic endotoxemia in patients with severe sepsis and Gram-negative bacteremia

In order to investigate the effect of carbapenems on systemic endotoxemia, 20 patients with severe sepsis due to ventilator-associated pneumonia and Gram-negative bacteremia were enrolled; 10 (group A) were administered 1 g t.i.d. of imipenem/cilastatin and 10 (group B) 2 g t.i.d. of meropenem. Blood was sampled at 0 time and after 1, 2, 4, 6, 12, 24, 36, 48, 60, 72, 84 and 96 hours for detection of endotoxins (LPS), interleukin-6 (IL-6), C-reactive protein (CRP) and drug levels. LPS were determined by the QCL-1000 LAL assay, IL-6 by an enzymeimmunoassay, CRP by nephelometry and carbapenem levels by a microbiological assay. We did not find that carbapenems had any effect on the kinetics of LPS and CRP; IL-6 of group A was lower than group B at 72 and 84 hours. No correlation was observed between drug levels of any carbapenem and LPS, IL-6 or CRP. It is concluded that in septic patients with Gram-negative bacteremia administration of either imipenem or meropenem did not affect systemic endotoxemia. The above data support the safe administration of both carbapenems in patients with severe sepsis.

Sequence requirements and an optimization strategy for short antimicrobial peptides

Short antimicrobial host-defense peptides represent a possible alternative as lead structures to fight antibiotic resistant bacterial infections. Bac2A is a 12-mer linear variant of the naturally occurring bovine host defense peptide, bactenecin, and demonstrates moderate, broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria as well as against the yeast Candida albicans. With the assistance of a method involving peptide synthesis on a cellulose support, the primary sequence requirements for antimicrobial activity against the human pathogen Pseudomonas aeruginosa of 277 Bac2A variants were investigated by using a luciferase-based assay. Sequence scrambling of Bac2A led to activities ranging from superior or equivalent to Bac2A to inactive, indicating that good activity was not solely dependent on the composition of amino acids or the overall charge or hydrophobicity, but rather required particular linear sequence patterns. A QSAR computational analysis was applied to analyze the data resulting in a model that supported this sequence pattern hypothesis. The activity of selected peptides was confirmed by conventional minimal inhibitory concentration (MIC) analyses with a panel of human pathogen bacteria and fungi. Circular-dichroism (CD) spectroscopy with selected peptides in liposomes and membrane depolarization assays were consistent with a relationship between structure and activity. An additional optimization process was performed involving systematic amino acid substitutions of one of the optimal scrambled peptide variants, resulting in superior active peptide variants. This process provides a cost and time effective enrichment of new candidates for drug development, increasing the chances of finding pharmacologically relevant peptides.

Release of exotoxin A, peptidoglycan and endotoxin after exposure of clinical Pseudomonas aeruginosa isolates to carbapenems in vitro

BACKGROUND

Production of several cell-associated components and extracellular enzymes can play important roles in the pathogenesis of Pseudomonas aeruginosa infections.

METHODS

We characterized the time course of morphological changes, production of exotoxin A (ETA) and release of peptidoglycan (PG) and endotoxin (ET) in clinical P. aeruginosa isolates after exposure to carbapenems including imipenem, panipenem, meropenem and biapenem at 0.5, 2, 8 and 32 microg/ml.

RESULTS

The amount of ETA in the supernatant of bacterial cultures exposed to carbapenems correlated with the number of viable cells, independently of morphological changes. Formation of ovoid cells and rapid cell lysis induced by carbapenems above the minimal inhibitory concentrations (MICs) decreased ETA production and ET release, while filamentation and prolonged cell lysis increased ETA production and/or ET release. Neither the number of viable cells nor bacterial morphology was related to the amount of PG released throughout the 6-hour observation period.

CONCLUSION

Exposure to concentrations of carbapenems above the MIC resulted in rapid cell lysis of P. aeruginosa and decreased ETA levels and ET release, while filamentation and prolonged cell lysis induced by exposure to sub-MICs of carbapenems were associated with increased ETA production and/or greater ET release.

Porcine reproductive and respiratory syndrome virus infection increases CD14 expression and lipopolysaccharide-binding protein in the lungs of pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) is a respiratory virus of swine that plays an important role in multifactorial respiratory disease. European strains of PRRSV cause mild or no respiratory signs on their own, but can sensitize the lungs for the production of proinflammatory cytokines and respiratory signs upon exposure to bacterial lipopolysaccharides (LPS). The inflammatory effect of LPS depends on the binding to the LPS receptor complex. Therefore, we quantified the levels of CD14 expression and LPS-binding protein (LBP) in the lungs of pigs throughout a PRRSV infection. Twenty-four gnotobiotic pigs were inoculated intranasally with PRRSV (10(6) 50% tissue culture infectious doses per pig, Lelystad strain) or phosphate-buffered saline (PBS), and euthanized 1-52 days later. Lungs were examined for CD14 expression (immunofluorescence and image analysis), LBP (ELISA), and virus replication. PRRSV infection caused a clear increase of CD14 expression from 3 to 40 days post-inoculation (DPI) and LBP from 7 to 14 DPI. Both parameters peaked at 9-10 DPI (40 and 14 times higher than PBS control pigs, respectively) and were correlated tightly with virus replication in the lungs. Double immunofluorescence labelings demonstrated that resident macrophages expressed little CD14 and that the increase of CD14 expression in the PRRSV-infected lungs was probably due to infiltration of highly CD14-positive monocytes in the interstitium. As both CD14 and LBP potentiate the inflammatory effects of LPS, their increase in the lungs could explain why PRRSV sensitizes the lungs for the production of proinflammatory cytokines and respiratory signs upon exposure to LPS.

Clinical laboratory differentiation of infectious versus non-infectious systemic inflammatory response syndrome

OBJECTIVE

To evaluate the accuracy of C-reactive protein (CRP), procalcitonin (PCT), neopterin, and endotoxin in the differential diagnosis of sepsis and non-infectious systemic inflammatory response syndrome (SIRS).

METHODS

A Medline database and references from identified articles were used to perform a literature search relating to the differential diagnosis of sepsis versus non-infectious SIRS.

RESULTS

CRP, PCT, and neopterin are released both in sepsis and in non-infectious inflammatory disease. CRP and PCT are equally effective, although not perfect, in differentiating between sepsis and non-infectious SIRS. However, CRP and PCT have different kinetics and profiles. The kinetics of CRP is slower than that of PCT, and CRP levels may not further increase during more severe stages of sepsis. On the contrary, PCT rises in proportion to the severity of sepsis and reaches its highest levels in septic shock. PCT tends to be higher in nonsurvivor than in survivor. Therefore, PCT demonstrated a closer correlation with the severity of sepsis and outcome than CRP. Unlike CRP and PCT, neopterin is increased in viral infection as well as bacterial infection, and neopterin is also a useful indicator of sepsis. Endotoxemia was detected in no more than half of patients with Gram-negative bacteremia, and Gram-negative bacteremia was detected in half of patients with endotoxemia.

CONCLUSIONS

The diagnostic capacity of PCT is superior to that of CRP due to the close correlation between PCT levels and the severity of sepsis and outcome. Neopterin is very useful in the diagnosis of viral infection. The endotoxin assay in combination with CRP, PCT, or neopterin may help as a diagnostic marker for Gram-negative bacterial infection.

The combination of PRRS virus and bacterial endotoxin as a model for multifactorial respiratory disease in pigs

This paper reviews in vivo studies on the interaction between porcine reproductive and respiratory syndrome virus (PRRSV) and LPS performed in the authors' laboratory. The main aim was to develop a reproducible model to study the pathogenesis of PRRSV-induced multifactorial respiratory disease. The central hypothesis was that respiratory disease results from an overproduction of proinflammatory cytokines in the lungs. In a first series of studies, PRRSV was shown to be a poor inducer of TNF-alpha and IFN-alpha in the lungs, whereas IL-1 and the anti-inflammatory cytokine IL-10 were produced consistently during infection. We then set up a dual inoculation model in which pigs were inoculated intratracheally with PRRSV and 3-14 days later with LPS. PRRSV-infected pigs developed acute respiratory signs for 12-24h upon intratracheal LPS inoculation, in contrast to pigs inoculated with PRRSV or LPS only. Moreover, peak TNF-alpha, IL-1 and IL-6 titers were 10-100 times higher in PRRSV-LPS inoculated pigs than in the singly inoculated pigs and the cytokine overproduction was associated with disease. To further prove the role of proinflammatory cytokines, we studied the effect of pentoxifylline, a known inhibitor of TNF-alpha and IL-1, on PRRSV-LPS induced cytokine production and disease. The clinical effects of two non-steroidal anti-inflammatory drugs (NSAIDs), meloxicam and flunixin meglumine, were also examined. Pentoxifylline, but not the NSAIDs, significantly reduced fever and respiratory signs from 2 to 6h after LPS. The levels of TNF-alpha and IL-1 in the lungs of pentoxifylline-treated pigs were moderately reduced, but were still 26 and 3.5-fold higher than in pigs inoculated with PRRSV or LPS only. This indicates that pathways other than inhibition of cytokine production contributed to the clinical improvement. Finally, we studied a mechanism by which PRRSV may sensitize the lungs for LPS. We hypothesized that PRRSV would increase the amount of LPS receptor complex in the lungs leading to LPS sensitisation. Both CD14 and LPS-binding protein, two components of this complex, increased significantly during infection and the amount of CD14 in particular was correlated with LPS sensitisation. The increase of CD14 was mainly due to infiltration of strongly CD14-positive monocytes in the lungs. The PRRSV-LPS combination proved to be a simple and reproducible experimental model for multifactorial respiratory disease in pigs. To what extent the interaction between PRRSV and LPS contributes to the development of complex respiratory disease is still a matter of debate.

The efficacy of bovine lactoferrin in the treatment of cows with experimentally induced Escherichia coli mastitis

The effect of bovine lactoferrin (Lf) was studied in experimental Escherichia coli mastitis, using enrofloxacin as a comparator. Mastitis was induced in six clinically healthy primiparous dairy cows by infusing 1500 colony-forming units of E. coli into a single udder quarter. The challenge was repeated into a contralateral quarter of the same cows 3 weeks later. At the first challenge, three cows were treated with 1.5 g of bovine lactoferrin intramammarily three times (12, 20 and 36 h postchallenge, PC), and the other three cows received 5 mg/kg of enrofloxacin (Baytril) parenterally (12, 36 and 60 h PC). Flunixin meglumine (2.2 mg/kg) was administered to all cows twice at 24-h intervals. During the second challenge, the treatments for the two groups were reversed. Intramammary challenge with E. coli produced clinical mastitis in all cows, but the severity of the disease varied markedly. No statistically significant differences between treatment groups were observed in clinical signs such as rectal temperature, rumen motility and general attitude. Milk somatic cell count, daily milk yield and bacterial counts in cows treated with Lf and those receiving enrofloxacin also did not differ significantly. However, a trend for a more rapid elimination of bacteria was seen in the cows treated with enrofloxacin. Milk NAGase activity also decreased significantly faster in the group treated with enrofloxacin. The concentration of lipopolysaccharide in milk compared with the number of bacteria was significantly lower in Lf than in enrofloxacin-treated cows (20 h PC).

Targeting of scavenger receptor class B type I by synthetic amphipathic alpha-helical-containing peptides blocks lipopolysaccharide (LPS) uptake and LPS-induced pro-inflammatory cytokine responses in THP-1 monocyte cells

Human scavenger receptor class B type I, CLA-1, mediates lipopolysaccharide (LPS) binding and internalization (Vishnyakova, T. G., Bocharov, A. V., Baranova, I. N., Chen, Z., Remaley, A. T., Csako, G., Eggerman, T. L., and Patterson, A. P. (2003) J. Biol. Chem. 278, 22771-22780). Because one of the recognition motifs in SR-B1 ligands is the anionic amphipathic alpha-helix, we analyzed the effects of model amphipathic alpha-helical-containing peptides on LPS uptake and LPS-stimulated cytokine production. The L-37pA model peptide, containing two class A amphipathic helices, bound with high affinity (K(d) = 0.94 microg/ml) to CLA-1-expressing HeLa cells with a 10-fold increased capacity when compared with mock transfected HeLa cells. Both LPS and L-37pA colocalized with anti-CLA-1 antibody and directly bound CLA-1 as determined by cross-linking. SR-BI/CLA-1 ligands such as HDL, apoA-I, and L-37pA efficiently competed against iodinated L-37pA. Bacterial LPS, lipoteichoic acid, and hsp60 also competed against iodinated L-37pA. Model peptides blocked uptake of iodinated LPS in both mock transfected and CLA-1-overexpressing HeLa cells. Bound and internalized Alexa-L-37pA and BODIPY-LPS colocalized at the cell surface and perinuclear compartment. Both ligands were predominantly transported to the Golgi complex, colocalizing with the Golgi markers bovine serum albumin-ceramide, anti-Golgin97 antibody, and cholera toxin subunit B. A 100-fold excess of L-37pA nearly eliminated BODIPY-LPS binding and internalization. L-37pA and its d-amino acid analogue, D-37pA peptide were similarly effective in blocking LPS, Gram-positive bacterial wall component lipoteichoic acid and bacterial heat shock protein Gro-EL-stimulated cytokine secretion in THP-1 cells. In the same culture media used for the cytokine stimulation study, neither L-37pA nor D-37pA affected the Limulus amebocyte lysate activity of LPS, indicating that LPS uptake and cytokine stimulation were blocked independently of LPS neutralization. These results demonstrate that amphipathic helices of exchangeable apolipoproteins may represent a general host defense mechanism against inflammation.

Binding and internalization of lipopolysaccharide by Cla-1, a human orthologue of rodent scavenger receptor B1

Scavenger receptor, class B, type I (SR-BI) mediates selective uptake of high density lipoprotein (HDL) cholesteryl ester. SR-BI recognizes HDL, low density lipoprotein (LDL), exchangeable apolipoproteins, and protein-free lipid vesicles containing negatively charged phospholipids. Lipopolysaccharides (LPS) are highly glycosylated anionic phospholipids contributing to septic shock. Despite significant structural similarities between anionic phospholipids and LPS, the role of SR-BI in LPS uptake is unknown. Cla-1, the human SR-BI orthologue, was determined to be a LPS-binding protein and endocytic receptor mediating the binding and internalization of lipoprotein-free, monomerized LPS. LPS strongly competed with HDL, lipidfree apoA-I and apoA-II for HDL binding to the mouse RAW cells. Stably transfected HeLa cells expressing Cla-1-bound LPS with a Kd of about 16 microg/ml, and had a 3-4-fold increase in binding capacity and LPS uptake. Bodipy-labeled LPS uptake was found to initially accumulate in the plasma membrane and subsequently in a perinuclear region identified predominantly as the Golgi complex. Bodipy-LPS and Alexa-apoA-I had staining that colocalized on the cell surface and intracellularly indicating similar transport mechanisms. When associated with HDL, LPS uptake was increased in Cla-1 overexpressing HeLa cells by 5-10-fold. Cla-1-associated 3H-LPS uptake exceeded 125I-apolipoprotein uptake by 5-fold indicating a selective LPS uptake. Upon interacting with Cla-1 overexpressing HeLa cells, the complex (Bodipy-LPS/Alexa 488 apolipoprotein-labeled HDL) bound and was internalized as a holoparticle. Intracellularly, LPS and apolipoproteins were sorted to different intracellular compartments. With LPS-associated HDL, intracellular LPS co-localized predominantly with transferrin, indicating delivery to an endocytic recycling compartment. Our study reveals a close similarity between Cla-1-mediated selective LPS uptake and the recently described selective lipid sorting by rodent SR-BI. In summary, Cla-1 was found to bind and internalize monomerized and HDL-associated LPS, indicating that Cla-1 may play important role in septic shock by affecting LPS cellular uptake and clearance.

Cardiac inflammation and innate immunity in septic shock: is there a role for toll-like receptors?

Our current understanding of the pathogenesis of sepsis suggests that bacteria as well as bacterial-derived products activate an uncontrolled network of host-derived mediators such as proinflammatory cytokines (ie, tumor necrosis factor [TNF] and interleukin [IL]-1beta), which can ultimately lead to cardiovascular collapse and death. Despite the potentially important role that TNF and IL-1beta may play in producing cardiac dysfunction in human septic shock, little is known with regard to the basic biochemical mechanism(s) by which bacterial pathogens induce their expression in the heart. A major advance in understanding the early events that are downstream from bacterial-mediated signaling has been the identification of Toll-like receptors (TLRs). TLR-mediated signaling is known to activate the transcription factor nuclear factor-kappaB and to upregulate TNF expression. It has recently been shown that the heart expresses TLRs, raising the possibility that these receptors may be responsible for mediating the deleterious effects of bacterial pathogens on cardiac function. In this review, we will discuss the emerging role for TLRs in the pathogenesis of the cardiovascular collapse that occurs during sepsis.

Current treatment of sepsis and endotoxaemia

This article reviews the new criteria for selecting the proper antimicrobial agent and dosage regimen for standard treatment of severe sepsis, with the intention of preventing septic shock. After introducing new concepts on the pathogenesis of sepsis and septic shock, the authors analyse the parameters of beta-lactam antibacterial activity, the antibiotic-induced release of bacterial endotoxin and the interrelationships between pharmacokinetics and pharmacodynamics of antibiotics in the search for an optimum dosage regimen of antimicrobial mono- or polytherapy for severely ill septic patients admitted to the intensive care unit. The mortality rate resulting from severe bacterial sepsis, particularly that associated with shock, still approaches 50% in spite of appropriate antimicrobial therapy and optimum supportive care. Bacterial endotoxins that are part of the cell wall are one of the cofactors in the pathogenesis of sepsis and septic shock and are often induced by antimicrobial chemotherapy, even if administered rationally. Not all antimicrobial agents are equally capable of inducing septic shock; this is dependent on their mechanism of action rather than on the causative pathogen species. The quantity of endotoxin released depends on the drug dose and whether filaments or spheroplast formation predominate. Some antibiotics, such as carbapenems, ceftriaxone, cefepime, glycopeptides, aminoglycosides and quinolones, do not have the propensity to provoke septic shock because their rapid bacterial activity induces mainly spheroplast or fragile spheroplast-like bacterial forms.