Effect of polymyxin B on experimental shock from meningococcal and Escherichia coli endotoxins

Multi-Scale Analysis of the Toraymyxin Adsorption Cartridge Part II: Computational Fluid-Dynamic Study

Extracorporeal endotoxin removal by means of the Toraymyxin device is based on the ability of polymyxin B to bind endotoxins with a high specificity. The endotoxins/polymyxin molecular interactions were computationally analyzed in a parallel work (Part I). In this paper we investigate with a multi-scale approach the phenomena involving blood and plasma fluid dynamics inside the device. The macro- and mesoscale phenomena were studied by means of 3D models using computational fluid dynamics. The flow behavior in the sorbent material was focused, modeling the sorbent as a homogeneous porous medium at the macroscale level, or accounting for the realistic geometry of its knitted fibers at the mesoscale level. A microscale model was then developed to analyze the behavior of endotoxin molecules subjected to the competition of flow drag and molecular attraction by fibergrafted polymyxin B. The macroscale results showed that a very regular flow field develops in the sorbent, furthermore supplying the peak velocity to be input in the lower-scale model. The mesoscale analysis yielded the realistic range for wall shear stresses (WSSs) acting on fiber walls. With WSS values in the entire range, the results of the microscale analysis demonstrated that the capability of polymyxin B to capture endotoxin molecules from the flow extends at distances one order of magnitude greater than the characteristic distance of the stable intermolecular bond. We conclude that the use of an integrated, multi-scale analysis allows for a comprehensive understanding of the complex mechanisms involved in endotoxin sorption phenomena with immobilized polymyxin B.

Invited review: Neisseria meningitidis lipopolysaccharides in human pathology

Neisseria meningitidis causes meningitis, fulminant septicemia or mild meningococcemia attacking mainly children and young adults. Lipopolysaccharides (LPS) consist of a symmetrical hexa-acyl lipid A and a short oligosaccharide chain and are classified in 11 immunotypes. Lipid A is the primary toxic component of N. meningitidis . LPS levels in plasma and cerebrospinal fluid as determined by Limulus amebocyte lysate (LAL) assay are quantitatively closely associated with inflammatory mediators, clinical symptoms, and outcome. Patients with persistent septic shock, multiple organ failure, and severe coagulopathy reveal extraordinarily high levels of LPS in plasma. The cytokine production is compartmentalized to either the circulation or to the subarachnoid space. Mortality related to shock increases from 0% to > 80% with a 10-fold increase of plasma LPS from 10 to 100 endotoxin units/ml. Hemorrhagic skin lesions and thrombosis are caused by up-regulation of tissue factor which induces coagulation, and by inhibition of fibrinolysis by plasminogen activator inhibitor 1 (PAI-1). Effective antibiotic treatment results in a rapid decline of plasma LPS (half-life 1—3 h) and cytokines, and reduced generation of thrombin, and PAI-1. Early antibiotic treatment is mandatory. Three intervention trials to block lipid A have not significantly reduced the mortality of meningococcal septicemia.

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.

The TLR4 agonist fibronectin extra domain A is cryptic, exposed by elastase-2; use in a fibrin matrix cancer vaccine

Fibronectin (FN) is an extracellular matrix (ECM) protein including numerous fibronectin type III (FNIII) repeats with different functions. The alternatively spliced FN variant containing the extra domain A (FNIII EDA), located between FNIII 11 and FNIII 12, is expressed in sites of injury, chronic inflammation, and solid tumors. Although its function is not well understood, FNIII EDA is known to agonize Toll-like receptor 4 (TLR4). Here, by producing various FN fragments containing FNIII EDA, we found that FNIII EDA's immunological activity depends upon its local intramolecular context within the FN chain. N-terminal extension of the isolated FNIII EDA with its neighboring FNIII repeats (FNIII 9-10-11) enhanced its activity in agonizing TLR4, while C-terminal extension with the native FNIII 12-13-14 heparin-binding domain abrogated it. In addition, we reveal that an elastase 2 cleavage site is present between FNIII EDA and FNIII 12. Activity of the C-terminally extended FNIII EDA could be restored after cleavage of the FNIII 12-13-14 domain by elastase 2. FN being naturally bound to the ECM, we immobilized FNIII EDA-containing FN fragments within a fibrin matrix model along with antigenic peptides. Such matrices were shown to stimulate cytotoxic CD8⁺ T cell responses in two murine cancer models.

Update on the management of neonatal sepsis in horses

Despite advances in neonatal intensive care sepsis, severe sepsis and septic shock remain the biggest killers of neonatal foals. Management of this severe syndrome remains difficult, requiring intensive intervention. Key aspects of management include infection control, hemodynamic support, immunomodulatory interventions, and metabolic/endocrine support. Infection control largely consists of early antimicrobial therapy, plasma transfusions, and local therapy for the infected focus. In cases with severe sepsis or septic shock, hemodynamic support with fluids, vasoactive agents, and respiratory support insuring oxygen delivery to vital organs is important. Nutritional support is important, but close monitoring is needed to avoid hyperglycemia and hypoglycemia.

Pedopeptins, novel inhibitors of LPS: taxonomy of producing organism, fermentation, isolation, physicochemical properties and structural elucidation

In the course of our screening for inhibitors of lipopolysaccharide (LPS) binding to cellular receptor CD14, potent inhibitory activity was detected in the cultured broth of Pedobacter sp. SANK 72003. Three active compounds, pedopeptin A, B and C, were isolated from the broth and their structures were elucidated by physicochemical and spectral data to be new cyclic depsipeptides.

Identification of cell-penetrating peptides that are bactericidal to Neisseria meningitidis and prevent inflammatory responses upon infection

Meningococcal disease is characterized by a fast progression and a high mortality rate. Cell-penetrating peptides (CPPs), developed as vectors for cargo delivery into eukaryotic cells, share structural features with antimicrobial peptides. A screen identified two CPPs, transportan-10 (TP10) and model amphipathic peptide (MAP), with bactericidal action against Neisseria meningitidis. Both peptides were active in human whole blood at micromolar concentrations, while hemolysis remained negligible. Additionally, TP10 exhibited significant antibacterial activity in vivo. Uptake of SYTOX green into live meningococci was observed within minutes after TP10 treatment, suggesting that TP10 may act by membrane permeabilization. Apart from its bactericidal activity, TP10 suppressed inflammatory cytokine release from macrophages infected with N. meningitidis as well as from macrophages stimulated with enterobacterial and meningococcal lipopolysaccharide (LPS). Finally, incubation with TP10 reduced the binding of LPS to macrophages. This novel endotoxin-inhibiting property of TP10, together with its antimicrobial activity in vivo, indicates the possibility to design peptide-based therapies for infectious diseases.

Pediatric sepsis: challenges and adjunctive therapies

Sepsis remains an important challenge in pediatric critical care medicine. This review provides an appraisal of adjunctive therapies for sepsis and highlights opportunities for meeting selected challenges in the field. Future clinical studies should address long-term and functional outcomes as well as acute outcomes. Potential adjunctive therapies such as corticosteroids, hemofiltration, hemoadsorption, and plasmapheresis may have important roles, but still require formal and more rigorous testing by way of clinical trials. Finally, the design of future clinical trials should consider novel approaches for stratifying outcome risks as a means of improving the risk-to-benefit ratio of experimental therapies.

Polymyxin B: a new strategy for multidrug-resistant Gram-negative organisms

BACKGROUND

There has been a renewed interest in using polymyxin B as a last resort therapeutic option, due to emergence of multidrug-resistant Gram-negative bacteria. Despite being available for clinical use for decades, there is still a very limited understanding on many aspects of this agent.

OBJECTIVE

To review what is known about polymyxin B and to identify missing information or gaps for future investigations.

METHODS

Pertinent information was reviewed from published literature in English.

RESULTS/CONCLUSION

For optimal use of polymyxin B, a more thorough understanding is needed on standardized susceptibility testing, serum and tissue concentrations achieved, antibacterial activity when polymyxin B is combined with other agents, and mechanisms of resistance. A more precise characterization of the relationship between drug concentration and toxicity is also required.

Innate-immunity cytokines induced by very small size proteoliposomes, a Neisseria-derived immunological adjuvant

Neisserial outer membrane proteins have been combined with monosialoganglioside GM3 to form very small size proteoliposomes (VSSP), a nanoparticulated formulation used as a cancer vaccine for the treatment of cancer patients with GM3-positive tumours. VSSP were shown to elicit anti-GM3 and anti-tumour immune responses. VSSP have also been shown to be an efficient adjuvant for tumour-cell and peptide-antigen vaccines in mice. In vitro studies showed that VSSP promote maturation of both murine and human dendritic cells, suggesting that VSSP could be used as efficient adjuvants. In order to study further the capacity of VSSP to elicit innate immune responses, human peripheral blood mononuclear cells and monocytes derived thereof were assessed for in vitro secretion of interleukin (IL)-10, IL-6, IL-12 and interferon (IFN)-gamma. VSSP most prominently induced the secretion of IL-6. IL-10 was secreted at a lower level. IL-12 p40 (but no p70) was also detected. IFN-gamma response was observed in 56% of the tested samples. Cytokine secretion was not related to lipopolysaccharide (LPS) content and involved Toll-like receptor 2 (TLR2)-mediated signal transduction. VSSP also induced DC maturation and a cytokine secretion pattern (high IL-6/low IL-10) which differs from that induced by LPS. The observed proinflammatory cytokine secretion pattern and the capacity of VSSP to drive DC maturation are examined in the light of the properties of other bacterial derivatives currently being user for immunotherapy purposes. Our results suggest that VSSP could be tested in clinical settings where T helper 1-type immune responses would be beneficial.

Evidence against a role for endotoxin in the hepatic encephalopathy of rats with thioacetamide-induced fulminant hepatic failure

BACKGROUND AND AIMS

Endotoxin has been proposed to participate in the development of hepatic encephalopathy. However, there is no published data concerning the effects of endotoxin neutralization on the degree of hepatic encephalopathy. The present study investigated the effect of chronic intraperitoneal injection of polymyxin B, a neutralizing antagonist of endotoxin, on hepatic encephalopathy in rats with thioacetamide (TAA)-induced fulminant hepatic failure.

METHODS

Male Sprague-Dawley rats weighing 300-350 g were used. Fulminant hepatic failure was induced by intraperitoneal injection of TAA (350 mg/kg/day) for 3 days. Two series of rats were designed to compare the effects of low dose (0.1 mg) or high dose (0.2 mg) intraperitoneal polymyxin B administration versus normal saline (NS) on hepatic encephalopathy. The injection was twice daily started from 2 days prior to TAA administration and lasted for 5 days. Severity of encephalopathy was assessed by the counts of motor activity in an Opto-Varimex animal activity meter. Plasma levels of endotoxin and tumor necrosis factor-alpha (an index of liver injury) were measured by Limulus assay and the ELISA method, respectively.

RESULTS

Neutralization of endotoxin by either low dose or high dose polymyxin B administration did not significantly alleviate the degree of hepatic encephalopathy, as represented by the counts of motor activities (P > 0.05). Plasma levels of endotoxin and tumor necrosis factor-alpha were comparable between rats treated with polymyxin B or NS (P > 0.05).

CONCLUSION

Our findings do not support the notion that endotoxin plays a major role in the pathogenesis of hepatic encephalopathy in rats with TAA-induced fulminant hepatic failure.

Pharmacodynamic evaluation of the neutralization of endotoxin by PMX622 in mice

Polymyxin B (PMB) binds to and neutralizes endotoxin, but its systemic clinical utility is limited by neuro- and nephrotoxicity. PMX622 is a covalent conjugate of PMB and Dextran-70 designed to retain the ability of PMB to neutralize endotoxin and to retain the favorable colloidal, pharmacokinetic, and metabolic properties of Dextran-70. PMX622 has demonstrated efficacy in a number of animal models and effectively neutralized endotoxin in phase I clinical trials. Here, we systematically evaluated the pharmacodynamic properties of PMX622 in a murine model of endotoxin-induced lethality in galactosamine-sensitized mice. PMX622 completely and dose dependently inhibited lethality in this model. A stoichiometric relationship was found between the endotoxin challenge dose and the dose of PMX622 needed for protection. PMX622 neutralized endotoxin from four different genera of gram-negative bacteria but not Neisseria meningitidis. PMX622 was significantly less toxic than PMB in the mouse, suggesting that PMX622 has a better margin of safety than PMB. The timing of PMX622 administration relative to endotoxin was crucial. PMX622 was active for several hours prior to the endotoxin challenge; however, PMX622 did not protect mice if administered >/=15 min after endotoxin challenge. This suggests that PMX622 would best be clinically used prophylactically rather than therapeutically. These studies will be crucial in designing and interpreting human clinical trials assessing PMX622 efficacy.

Human lipoproteins have divergent neutralizing effects on E. coli LPS, N. meningitidis LPS, and complete Gram-negative bacteria

The use of lipoproteins has been suggested as a treatment for Gram-negative sepsis because they inhibit lipopolysaccharide (LPS)-mediated cytokine production. However, little is known about the neutralizing effects of lipoproteins on cytokine production by meningococcal LPS or whole Gram-negative bacteria. We assessed the neutralizing effect of LDLs, HDLs, and VLDLs on LPS- or whole bacteria-induced cytokines in human mononuclear cells. A strong inhibition of Escherichia coli LPS-induced interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, and IL-10 by LDL and HDL was seen, whereas VLDL had a less pronounced effect. In contrast, Neisseria meningitidis LPS, in similar concentrations, was neutralized much less effectively than E. coli LPS. Effective neutralization of meningococcal LPS required a longer interaction time, a lower concentration of LPS, or higher concentrations of lipoproteins. The difference in neutralization was independent of the saccharide tail, suggesting that the lipid A moiety accounted for the difference. Minimal neutralizing effects of the lipoproteins were observed on whole E. coli or N. meningitidis bacteria under all conditions tested. These results indicate that efficient neutralization of LPS depends on the type of LPS, but a sufficiently long interaction time, a low LPS concentration, or high lipoprotein concentration also inhibited cytokines by the less efficiently neutralized N. meningitidis LPS. Irrespective of these differences, whole bacteria showed no neutralization by lipoproteins.

Stimulation of rat liver mitochondrial sn-glycerol-3-phosphate acyltrasferase by polymyxin B via enhanced extraction of lysophosphatidic acid

The purpose of this investigation was to determine how polymyxin B stimulates the activity of mitochondrial glycerophosphate acyltransferase. Polymyxin B did not change the integrity of the mitochondrial outer membrane as judged by testing the latency (>80%) of cytochrome oxidase activity. The stimulation totally disappeared when polymyxin B-treated mitochondria were washed. The FA side chain in polymyxin B was unnecessary for stimulation, as the nonapeptide was as effective as the whole antibiotic. The stimulation by polymyxin B or the nonapeptide was observed only in the presence of BSA. Cytochrome c, when added to the incubation medium instead of albumin, did not stimulate the mitochondrial enzyme, but did produce a stimulatory effect of polymyxin B on the mitochondrial acyltransferase. As reported earlier for the bacterial and microsomal acyltransferase, other polycationic compounds such as spermine and spermidine stimulated mitochondrial glycerophosphate acyltransferase. The stimulation of the mitochondrial acyltransferase by spermine and spermidine also occurred only in the presence of BSA. The analysis of the products of esterification demonstrated the presence of more lysophosphatidic acid (LPA) in the polymyxin B- and polyamine-stimulated assays in comparison to their respective control. Furthermore, in comparison to the albumin-treated control, there was 60% more LPA present in the assay supernatant fractions of polymyxin B-treated samples. Our results suggest that polymyxin B stimulates the mitochondrial glycerophosphate acyltransferase activity by enhancing the extraction of more LPA from the mitochondria to the supernatant fraction.

Clindamycin modulates inflammatory-cytokine induction in lipopolysaccharide-stimulated mouse peritoneal macrophages

We investigated the mechanism by which clindamycin (CLI) modulates cytokine induction after lipopolysaccharide (LPS) stimulation. Although CLI decreased the intracellular expression levels of tumor necrosis factor alpha and interleukin 1beta (IL-1beta) and increased IL-6 expression in macrophages, cytokine mRNA expression levels were similar in CLI-treated and untreated groups. Our findings suggest that CLI modulates cytokine production in LPS-stimulated macrophages.

Endotoxin removal by direct hemoperfusion with an adsorbent column using polymyxin B-immobilized fiber ameliorates systemic circulatory disturbance in patients with septic shock

Direct hemoperfusion (DHP) with an adsorbent column using polymyxin B-immobilized fiber (PMX-F) has been shown to improve the state of shock in patients with septic shock. However, no evidence has been presented for a direct link between endotoxin removal by DHP with PMX-F and improvement in septic shock. We retrospectively analyzed clinical profiles of 24 patients with septic shock (16 patients, gram-negative; 8 patients, non-gram-negative septic shock) who underwent DHP with PMX-F. Patients with gram-negative septic shock were characterized by hyperdynamic circulation. DHP with PMX-F reduced blood endotoxin concentrations and ameliorated shock, with an improvement in hyperdynamic circulation in patients with gram-negative septic shock. Mean arterial pressure also was elevated after therapy in patients with non-gram-negative septic shock, but systemic hemodynamics were unaffected. Regardless of the causative microorganism, patients with endotoxemia (blood endotoxin level > 10 pg/mL) showed hyperdynamic shock, and DHP with PMX-F reduced blood endotoxin levels and ameliorated hyperdynamic circulation, whereas patients without endotoxemia showed features of shock without hyperdynamic circulation, and DHP with PMX-F ameliorated shock without affecting cardiac performance. In patients with gram-negative septic shock, blood endotoxin concentration correlated positively with cardiac output and negatively with systemic vascular resistance before DHP therapy. Reduction in blood endotoxin concentration by DHP therapy positively correlated with the reduction in cardiac output. Our findings indicate that the improvement in hyperdynamic circulation was related directly to endotoxin removal by the PMX-F column, and endotoxin has an important role in the development of hyperdynamic circulation in patients with gram-negative septic shock.

The role of lipopolysaccharide in stimulating adrenomedullin production during polymicrobial sepsis

Previous studies have shown that adrenomedullin (AM), a potent vasodilatory peptide, is upregulated during sepsis. However, it remains unknown whether the increased AM observed under such conditions is solely due to the elevated levels of circulating lipopolysaccharide (LPS). To determine this, an Alzet micro-osmotic pump, containing a low dose of Escherichia coli LPS or vehicle (sterile normal saline), was implanted in the peritoneal cavity of the normal male adult rat. At 10 h after the pump implantation, samples of blood and small intestine were harvested for the determination of AM by radioimmunoassay. In additional groups, rats were subjected to polymicrobial sepsis by cecal ligation and puncture (CLP). LPS binding agent polymyxin B was administrated intramuscularly at 1 h prior to as well as 5 h after the onset of sepsis. At 10 h after CLP or sham-operation, blood and intestinal samples were harvested and levels of AM were then determined. Plasma levels of LPS were also measured by Limulus amebocyte lysate assay. The results indicate that administration of a low dose of LPS via the peritoneal cavity in normal animals (which did not significantly alter cardiac output, blood pressure or heart rate) markedly increased plasma and intestinal levels of AM. In addition, plasma and tissue levels of AM increased significantly at 10 h after CLP. Administration of polymyxin B, however, attenuated the increase in AM levels under such conditions. Similarly, the increased plasma levels of LPS was significantly reduced by polymyxin B during sepsis. These results, taken together, suggest that the upregulated AM observed during polymicrobial sepsis is at least in part due to the increase in circulating levels of endotoxin.

Pretreatment of mice with clindamycin improves survival of endotoxic shock by modulating the release of inflammatory cytokines

Suppression of endotoxin release and subsequent production of inflammatory cytokines is crucial in the treatment of septic shock. We investigated the effect of clindamycin (CLI) on endotoxic shock induced in mice by Escherichia coli lipopolysaccharide (LPS). Mice were treated with CLI (160 to 600 mg/kg) or saline and then injected with E. coli LPS and D-(+)-galactosamine intraperitoneally 0.5 h after CLI administration. Pretreatment with CLI significantly improved survival in a dose-dependent manner (CLI, at 160, 300, and 440 mg/kg) and significantly lowered the peak concentrations of tumor necrosis factor alpha and interleukin-1beta (IL-1beta) in serum. However, the peak concentrations of IL-6 in the sera of CLI-treated mice were higher than in control mice. Our findings suggest that CLI alters LPS-induced inflammatory cytokine production and suppresses endotoxin-induced mortality in this murine model.

Polymyxin B sulfate and colistin: old antibiotics for emerging multiresistant gram-negative bacteria

BACKGROUND

Polymyxin B sulfate and colistin, also known as colistimethate, have not been used for many years because less toxic antimicrobials are available. Gram-negative bacteria that are resistant to the aminoglycosides, beta-lactams, and fluoroquinolones are becoming more common. These bacteria are often susceptible to the polymyxins.

OBJECTIVE

To present a review of the chemistry, antibacterial spectrum, dosing, pharmacokinetics, toxicity, and indications for polymyxin B sulfate and colistin.

DATA SOURCE

A MEDLINE search (1966-1998) of the English-language literature was performed to identify primary literature on the polymyxins. Older citations ( 1949-1965) were identified through the bibliographies of these articles.

STUDY SELECTION

All available reports of in vitro antibacterial activity, animal and clinical trials, and case reports were reviewed.

DATA SYNTHESIS

The polymyxins are amphipathic molecules that interact with lipopolysaccharide in the bacterial outer membrane. They have potent antiendotoxic properties and antibacterial activity against Pseudomonas aeruginosa and many of the Enterobacteriaceae. Polymyxin B and colistin are usually given at a dose of 1.5-2.5 and 5 mg/kg/d, respectively, in two divided doses. Dosing must be altered in renal failure since the kidney is the primary route of elimination. Distribution into pleural fluid, joints, and cerebrospinal fluid is poor. Toxic effects involve the kidney and central nervous system. The polymyxins are recommended for serious systemic infections caused by gram-negative bacteria that are resistant to other agents.

CONCLUSIONS

Polymyxin B sulfate and colistin have a role in the therapy of multidrug-resistant gram-negative bacterial infections.

Evidence against a role for endotoxin in the hyperdynamic circulation of rats with prehepatic portal hypertension

BACKGROUND/AIMS

Excessive formation of nitric oxide may mediate the generalized vasorelaxation and hyporesponsiveness to vasoconstrictors observed in portal hypertensive states. Endotoxin, released from the bowel and detoxified by the liver, could stimulate inducible nitric oxide synthase directly or indirectly via the cytokine cascade. This study investigated the effect of chronic intraperitoneal injection of polymyxin B, a neutralizing antagonist of endotoxin, on the hemodynamics of partially portal vein-ligated (PVL) rats.

METHODS

Concomitantly with endotoxin (600 EU) and dactinomycin (80 microg), polymyxin B (0.1 mg) or normal saline (N/S) was administered via an intraperitoneal route to male Sprague-Dawley rats. Twenty-four hours later, mean arterial pressure was determined. In PVL rats polymyxin B (0.1 mg in 5 cc N/S) or N/S was given intraperitoneally twice daily from 2 days prior to operation until 5 days (short-term) or 14 days (long-term) after the operation. Long-term polymyxin B- or N/S-treated sham-operated rats were included as controls. Hemodynamic studies with a thermodilution technique were performed at the end of treatment. Blood samples were collected from another series of PVL rats with long-term treatment to determine plasma levels of endotoxin and tumor necrosis factor-alpha. Plasma levels of endotoxin and tumor necrosis factor-alpha were measured by Limulus assay and the ELISA method, respectively.

RESULTS

With the dosage of 0.1 mg polymyxin B, hypotension in rats subjected to endotoxin and dactinomycin administration could be corrected (polymyxin B vs. placebo: 130.0+/-7.7 vs. 108.8+/-6.7 mm Hg, p<0.05). However, long-term or short-term treatment with the same dosage of polymyxin B failed to ameliorate the hyperdynamic circulation of PVL rats. In addition, long-term treatment with polymyxin B did not change systemic and portal hemodynamics in sham-operated rats. Plasma levels of endotoxin and tumor necrosis factor-alpha were comparable in PVL rats treated with long-term polymyxin B or N/S (p>0.05).

CONCLUSIONS

Our findings do not support the role of endotoxin in the hyperdynamic circulation of PVL rats.

Induction of nitric oxide synthase in vivo and cell injury in rat duodenal epithelium by a water soluble extract of Helicobacter pylori

1. Helicobacter pylori (Hp) infection, which involves the gastric antrum and duodenal mucosa, may be involved in peptic ulceration by stimulating the local release of cytoxic or pro-inflammatory factors. 2. Nitric oxide (NO) is known to be cytotoxic at high concentration. The aim of the present study was therefore to investigate the ability of a water soluble extract of Hp to induce NO synthase in duodenal mucosa and epithelial cells following its administration in vivo in rats and determine its association with cell damage. 3. Administration of Hp water extract (4 ml kg(-1)) led to the expression of the calcium-independent inducible nitric oxide synthase (iNOS) after 4 h in the duodenum, determined as [14C]-arginine conversion to citrulline. 4. This iNOS activity was not reduced by pretreatment with anti-neutrophil serum (0.4 ml kg(-1), i.p., 3 h before challenge). However, dexamethasone pretreatment (1 mg kg(-1), i.v., 2 h before the extract), or administration of the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 5 mg kg(-1), i.v., 2.5 h after the extract) reduced this activity. 5. Furthermore, iNOS was expressed in duodenal isolated epithelial cells 4 h after the i.v. challenge with the extract, at a time when the cellular viability was also reduced, as assessed by trypan blue exclusion. 6. Dexamethasone pretreatment, administration of L-NAME, or pretreatment with polymyxin B (1 mg kg(-1), i.v.) which binds endotoxin, reduced both the iNOS activity and epithelial cell damage. 7. The induction of NO synthase by the Hp extract thus results in duodenal epithelial cell injury and such actions could play a role in pathogenesis of peptic ulcer disease.

Extracorporeal adsorbent-based strategies in sepsis

Gram-negative bacterial sepsis remains a challenging diagnostic and therapeutic dilemma to the practicing clinician. Bacterial-derived products (eg, gram-negative bacterial lipopolysaccharide or endotoxin) and host inflammatory mediators (eg, tumor necrosis factor-alpha and interleukin-1) are believed to play a pivotal role in the pathogenesis of sepsis and septic shock. Despite the many advances in the treatment of sepsis, mortality rates in septic patients remain high. Indeed, numerous clinical trials using biologically engineered immunotherapies targeting specific inflammatory mediators have proven unsuccessful. This lack of success has led to a renewed interest in blood purification techniques using extracorporeal therapies. During sepsis, circulating bacterial-derived products as well as inflammatory mediators can be reduced and/or eliminated by various extracorporeal adjunctive therapies such as plasma exchange, continuous renal replacement, and adsorbent-based therapies. Adsorbents have commonly been used orally for gastrointestinal removal of toxins or drugs. However, their potential use in sepsis has received little attention. The incorporation of adsorbents in hemoperfusion columns has allowed their use for the removal of toxic compounds from the circulatory system. Adsorbents developed for use in sepsis can bind toxins in a nonselective (eg, charcoal), selective (eg, polymyxin B-immobilized polystyrene-derivative fiber), or specific (eg, antibody-coated microsphere-based detoxification system) way. However, despite an explosive development in the experimental use of these promising therapies, randomized clinical trials are currently lacking. In summary, a multi-disciplinary complex therapeutic approach remains a prerequisite to the successful treatment of sepsis.

Introducing Critical Appraisal to studies of animal models investigating novel therapies in sepsis

OBJECTIVES

To discuss theoretical and practical aspects relating to the design of animal studies investigating the efficacy of novel therapeutic agents for the treatment of sepsis, and to make explicit the process whereby these studies can be evaluated for the purpose of designing clinical trials in humans.

DATA SOURCES

Relevant articles from the pertinent literature were reviewed.

STUDY SELECTION

Studies relevant to an evidence-based assessment of clinical studies on therapeutic efficacy, and studies relevant to the design of animal models of sepsis were selected.

DATA EXTRACTION

Concepts relevant to an evidence-based assessment of the animal literature were extracted.

DATA SYNTHESIS

Articles were reviewed and an evidence-based framework for the assessment of animal studies was developed. In this process, we discuss the steps that are necessary to assess the internal validity of an individual study and review topics relevant to the application of animal data to the design of clinical trials.

CONCLUSIONS

The success of clinical trials of sepsis therapies is predicated on the generation and interpretation of sound preclinical data. In this review, we have attempted to outline an evidence-based approach to the assessment of preclinical animal studies evaluating novel therapeutic interventions in sepsis.

Effect of rhinovirus 39 (RV-39) infection on immune and inflammatory parameters in allergic and non-allergic subjects

The economic impact and medical complication rate of the common cold are well documented, but many of the physiological, inflammatory, and immune responses to common cold viruses have only recently been investigated. The purpose of this study was to compare selected systemic immune and inflammatory responses to experimental rhinovirus (RV)-39 challenge in seronegative allergic rhinitis and non-allergic rhinitis subjects. Peripheral blood was obtained before (baseline), during (acute), and 23 days after (convalescent) RV-39 intranasal challenge and assayed for leucocyte histamine release, serum immunoglobulins, allergen-specific IgE antibodies, plasma histamine, and platelet aggregation. All subjects were infected, as manifested by viral shedding in nasal secretions or seroconversion. RV-39 infection induced significant acute increases in serum IgE, leucocyte histamine release, and platelet aggregation, but caused no changes in serum IgG, serum IgA, serum IgM, and plasma histamine. The first change was confined to the allergic rhinitis subjects. There was no evidence that the acute rise in total serum IgE was due to an elevation of a pre-existing, pollen-specific serum IgE antibody. The results show that intranasal challenge with RV-39 induced changes in systemic immune and inflammatory parameters with a unique response pattern in allergic rhinitis subjects.

Endotoxemia: methods of detection and clinical correlates

As an assay for endotoxin, the Limulus amebocyte lysate assay has several desirable properties: sensitivity, specificity, and potential for adaptation to a quantitative format. Several modifications have been developed to enhance its potential for clinical application. The modifications that allow quantitative measurement of endotoxin and also improve its application to blood samples are described in this review. In fluids other than blood, the detection of endotoxin with the Limulus amebocyte lysate assay can be used as an aid to identify the presence of gram-negative bacteria, and the assay has established utility. With blood, however, there are a range of factors that interfere with the detection of endotoxemia and there are disparate views with respect to the diagnostic and prognostic significance of the test results. In general, the clinical significance of the finding of endotoxemia broadly parallels the frequency and importance of gram-negative sepsis in the patient groups studied and a decline in endotoxin levels accompanies clinical improvement. However, with therapies designed to reduce levels of endotoxin, or to antagonize its effects, it is unclear whether clinical improvement occurs as a consequence of changes in the levels of endotoxemia.

Polymyxin B stimulates production of complement components and cytokines in human monocytes

Polymyxin B (PmB), an agent often used to neutralize the effects of bacterial lipopolysaccharide (LPS), was shown to exert a dose-dependent stimulatory effect on the biosynthesis of C3, factor B, interleukin-6 (IL-6), and granulocyte-macrophage colony-stimulating factor (GM-CSF) in human monocytes. A low dose of PmB (1 to 5 micrograms/ml) efficiently suppressed the LPS-induced (1 or 100 ng/ml) production of IL-6, GM-CSF, and factor B, but not the C3 production induced by 100 ng of LPS per ml. A reduced level of GM-CSF may have contributed to the persisting high C3 concentrations and the apparent lack of LPS inhibition in the latter situation, since GM-CSF is an inhibitor of monocyte C3 biosynthesis.

Inhibition of endotoxin-induced interleukin 8 release by teicoplanin in human whole blood

Antibiotic-induced endotoxin (lipopolysaccharide; LPS) release may precipitate septic shock. In the present study the effect of teicoplanin, which has been reported to neutralize LPS in experimental models, on LPS neutralization was investigated in human whole blood samples. Levels of interleukin 8, a preinflammatory cytokine which was stimulated by Salmonella minnesota R595 LPS (12.6 micrograms/ml), were monitored over time. Interleukin 8 concentrations increased over time up to 24 h. When LPS was preincubated with teicoplanin (antibiotic: LPS ratio 20:1, w/w), interleukin 8 concentrations were found significantly (p < 0.05) reduced at 4, 8 and 24 h after LPS challenge. Interleukin 1 beta (at 4, 8 and 24 h) and tumor necrosis factor alpha (at 8 and 24 h) levels were also significantly decreased by teicoplanin. In this experiment model, a teicoplanin:LPS ratio 100-fold less than the ratio achievable in plasma of septic shock patients was able to reduce interleukin 8, which has been correlated with the severity of septic disease.

Polymyxin B-horseradish peroxidase conjugates as tools in endotoxin research

The peptide antibiotic Polymyxin B (PMB) binds to bacterial endotoxin (lipopolysaccharide, LPS). We prepared covalent conjugates of PMB and horseradish peroxidase (HRP) by periodation of HRP-linked oligosaccharides followed by direct condensation with PMB. In addition we prepared monoclonal antibodies (Mabs) to PMB. The PMB-HRP conjugates and anti-PMB Mabs were used to study in ELISA the binding of PMB to LPS from Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. In addition, PMB-HRP was used to quantify lipid A in ELISA, and to stain gram-negative bacteria histochemically. For the study of PMB-LPS interaction, PMB-HRP proved to be superior to the anti-PMB Mabs. PMB-HRP conjugates are useful general probes to detect or measure lipid A and LPS of various species using very simple methods and to stain bacteria, and they may obviate the need for many specific antisera. Thus, PMB-HRP conjugates are useful probes for endotoxin research.

Alpha 1-acid glycoprotein potentiates lipopolysaccharide-induced secretion of interleukin-1 beta, interleukin-6 and tumor necrosis factor-alpha by human monocytes and alveolar and peritoneal macrophages

Although the physiological role of alpha 1-acid glycoprotein (AGP), an acute-phase protein, is poorly understood, several lines of evidence support a modulatory action on the immune response. In this study, we investigated the effect of AGP on the production of interleukin (IL)-1 beta, IL-6 and tumor necrosis factor (TNF)-alpha by human monocytes, macrophages and the monocytic THP-1 cell line. AGP significantly enhanced (2- to 7-fold) the production of these cytokines in monocytes induced by suboptimal concentrations of lipopolysaccharide [E. coli lipopolysaccharide (LPS): 100 ng/ml] in serum-free conditions, whereas it had little or no effect in the absence of LPS. The potentiating effect of AGP was inhibited by specific antibodies. It was concentration dependent and the greatest enhancement was observed with 250-500 micrograms/ml. Moreover, AGP only potentiated the effect of suboptimal concentrations of LPS. AGP did not alter the time course of LPS-induced IL-1 beta, IL-6 or TNF-alpha secretion. AGP acts as a co-inducer and could also potentiate cytokine secretion triggered by Neisseria meningitidis LPS and muramyl dipeptide. The glycan moiety of AGP did not seem to be involved in its potentiating effect, since both its major glycoforms and asialo-AGP potentiated the effect of LPS to the same extent as native AGP. Possible differences in the effect of AGP according to cell maturation were investigated using isolated human macrophages: AGP potentiated LPS-induced cytokine production by both peritoneal and alveolar macrophages. These data suggest that AGP can modulate monocyte/macrophage functions, thereby contributing to the amplification and regulation of immune and inflammatory responses.