Effects of extracellular pH on tumour necrosis factor-alpha production by resident alveolar macrophages

Cellular acid-base status has been found to exert selective actions on the effector functions of activated macrophages (mphi). We examined the effects of extracellular pH (pH(o)) on the production of tumour necrosis factor-alpha (TNF-alpha) induced by lipopolysaccharide (LPS) in resident alveolar mphi. Cells were obtained by bronchoalveolar lavage of rabbits, activated in vitro with LPS, and cultured at pH(o) 5.5, 6.5 or 7.4 for up to 18 h. The relative abundance of TNF-alpha mRNA peaked at approximately 2 h. The peak transcript abundance was increased at lower pH(o) values. This finding probably reflected pre-transcription/transcription effects of pH, in as much as the stability of TNF-alpha mRNA induced with phorbol ester was unaffected by the experimental pH(o) values. TNF-alpha secretion by LPS-treated mphi decreased at lower pH(o) values. The TNF-alpha content of mphi-conditioned media decreased progressively with decrements in pH(o). The reduced TNF-alpha secretion at pH(o) 5.5 was accompanied by an increase in the cytosolic TNF-alpha content (compared with that at pH(o) 7.4), indicating that pH(o) altered TNF-alpha secretion due, in part, to the intracellular retention of synthesized cytokine (i.e. a post-translation effect). The data show that pH(o) has multiple effects (pre-transcription/transcription and post-translation) on TNF-alpha production induced by LPS in resident alveolar mphi. These results suggest that the role of alveolar mphi in inflammatory responses is modulated by pH(o), which may be important in tumours/abscesses and sites of infection where the external milieu is acidic.

Cholera toxin-induced PGE(2) activity is reduced by chemical reaction with L-histidine

Mediators of cholera toxin (CT)-induced fluid secretion include 3',5'-adenosine monophosphate (cAMP), prostaglandin E(2) (PGE(2)), and 5-hydroxytryptamine (5-HT). Administration of L-histidine significantly reduced the net secretory response of the small intestine of mice challenged with CT and reduced the capacity of PGE(2) to stimulate Na+ transport in Ussing chambers. We demonstrated that L-histidine chemically modified the structure of PGE(2) but had no direct effect on cAMP or 5-HT. L-Histidine and imidazole reacted with PGE(2) in vitro in cell-free mixtures incubated at 37 degrees C and pH 7.0 under an atmosphere of N(2) with the formation of PGE(2)-imidazole and PGE(2)-histidine covalent adducts. Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) analysis of the purified adduct showed that imidazole catalyzed the dehydration of PGE(2). A Michael adduct then was formed between C11 of 11-deoxy-Delta(10) PGE(2) (PGA(2)) and the tau nitrogen in the imidazole ring of L-histidine. Importantly, the isolated PGE(2)-imidazole and PGE(2)-histidine adducts inhibited CT-induced fluid loss and cAMP accumulation in mouse intestinal loops. The protection provided by PGE(2)-imidazole, PGE(2)-histidine, and L-histidine against intestinal fluid loss could provide a basis for future therapy against cholera.

Post-transcriptional effects of extracellular pH on tumour necrosis factor-alpha production in RAW 246.7 and J774 A.1 cells

The present studies determined the effects of extracellular pH (pH(o)) on the production of tumour necrosis factor-alpha (TNF-alpha) in the macrophage-like cell lines RAW 246.7 and J774 A.1. The cells were activated with lipopolysaccharide (LPS) at pH(o) 5.5, 6.5 or 7.4. TNF-alpha gene transcription was monitored by Northern blot analysis. Synthesis of the cytokine was monitored by ELISA measurements of the TNF-alpha content of cell-conditioned media (extracellularly released TNF-alpha) and cell lysates (cytosolic TNF-alpha). The magnitude of the TNF-alpha response differed markedly between the two cell lines. RAW cells were more responsive to LPS than were J774 cells. However, the effects of pH(o) on TNF-alpha production were similar in the two cell lines. TNF-alpha gene transcription was insensitive to experimental pH(o). The pH(o) had no effect on the abundance of TNF-alpha mRNA at 2, 4 or 18 h. Nonetheless, synthesis of TNF-alpha was affected significantly by pH(o). The TNF-alpha contents of cell-conditioned medium and cell lysate at 18 h were reduced progressively at lower pH(o) values. The data indicate that pH(o) alters TNF-alpha production in RAW and J774 cells at a post-transcriptional level. These findings suggest that pH(o) influences the phenotypic responses of macrophages to activating stimuli and modifies the role that macrophages play in inflammatory and immune actions.

Prostaglandin levels in stimulated macrophages are controlled by phospholipase A2-activating protein and by activation of phospholipase C and D

Prostaglandins (PG), which are responsible for a large array of biological functions in eukaryotic cells, are produced from arachidonic acid by phospholipases and cyclooxygenase enzymes COX-1 and COX-2. We demonstrated that PG levels in cells were partly controlled by a regulatory protein, phospholipase A2 (PLA2)-activating protein (PLAA). Treatment of murine macrophages with lipopolysaccharide, interleukin-1beta, and tumor necrosis factor-alpha increased PLAA levels at early time points (2-30 min), which correlated with an up-regulation in cytosolic PLA2 and PGE2 levels. Both COX-2 and secretory PLA2 were also increased in lipopolysaccharide-stimulated macrophages, however, at later time points of 4-24 h. The role of PLAA in eicosanoid formation in macrophages was confirmed by the use of an antisense plaa oligonucleotide. Within amino acid residues 503-538, PLAA exhibited homology with melittin, and increased PGE(2) production was noted in macrophages stimulated with melittin. In addition to PLA2, we demonstrated that activation of phospholipase C and D significantly controlled PGE2 production. Finally, increased antigen levels of PLAA, COX-2, and phospholipases were demonstrated in biopsy specimens from patients with varying amounts of intestinal mucosal inflammation, which corresponded to increased levels of phospholipase activity. These results could provide a basis for the development of new therapeutic tools to control inflammation.

Melittin-mediated release of [3H]-oleic acid from E. coli cells is dependent upon heat- and trypsin-sensitive factor(s) in human serum

Synthetic melittin mediated the release of [3H]-oleic acid ([3H]-OA) or its acylated lipids from [3H]-OA-labeled E. coli cells exposed to human serum. This phenomenon was not observed in the absence of serum and was calcium independent. The addition of serum was not required for melittin-mediated lysis of erythrocytes, although lysis was greater in the presence of serum than in its absence (P<0.001). Trypsin treatment of human serum reduced the melittin-mediated release of [3H]-OA/acylated lipids, and this effect was more pronounced upon boiling the serum (P<0.01). A kinetic study showed that maximum release of [3H]-OA/acylated lipids occurred within 3-6 min. Thin layer chromatography (TLC) analysis showed the lipids to be phosphatidyl ethanolamine (PE), phosphatidylethanol (PEt) and phosphatidic acid (PA). There was no detectable level of oleic acid (OA), diacylglycerol (DAG), phosphatidyl choline (PC) or phosphatidyl serine (PS). These findings suggested that a trypsin and heat-sensitive enzyme/factor present in the serum had a role in melittin-mediated action. These findings further showed that melittin activated phospholipase D (PLD), without affecting phospholipase A(2) (PLA(2)) or phospholipase C (PLC) activity.

The cytotoxic enterotoxin of Aeromonas hydrophila induces proinflammatory cytokine production and activates arachidonic acid metabolism in macrophages

An aerolysin-related cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses multiple biological activities, which include its ability to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. The role of Act in the virulence of the organism has been demonstrated. In this study, we evaluated the potential of Act to induce production of proinflammatory cytokines associated with Act-induced tissue injury and Act's capacity to activate in macrophages arachidonic acid (AA) metabolism that leads to production of eicosanoids (e.g., prostaglandin E(2) [PGE(2)]). Our data indicated that Act stimulated the production of tumor necrosis factor alpha and upregulated the expression of genes encoding interleukin-1beta (IL-1beta) and IL-6 in the murine macrophage cell line RAW264.7. Act also activated transcription of the gene encoding inducible nitric oxide synthase. Act evoked the production of PGE(2) coupled to the cyclooxygenase-2 (COX-2) pathway. AA is a substrate for PGE(2), and Act produced AA from phospholipids by inducing group V secretory phospholipase A(2). We also demonstrated that Act increased cyclic AMP (cAMP) production in macrophages. cAMP, along with PGE(2), could potentiate fluid secretion in animal models because of infiltration and activation of macrophages resulting from Act-induced tissue injury. After Act treatment of RAW cells, we detected an increased translocation of NF-kappaB and cAMP-responsive element binding protein (CREB) to the nucleus using gel shift assays. Act also upregulated production of antiapoptotic protein Bcl-2 in macrophages, suggesting a protective role for Bcl-2 against cell death induced by proinflammatory cytokines. The increased expression of genes encoding the proinflammatory cytokines, COX-2, and Bcl-2 appeared correlated with the activation of NF-kappaB and CREB. This is the first report of the detailed mechanisms of action of Act from A. hydrophila.

Neutrophil activation by bacterial lipoprotein versus lipopolysaccharide: differential requirements for serum and CD14

Neutrophil activation plays an important role in the inflammatory response to Gram-negative bacterial infections. LPS has been shown to be a major mediator of neutrophil activation which is accompanied by an early down-regulation of L-selectin and up-regulation of CD1lb/CD18. In this study, we investigated whether lipoprotein (LP), the most abundant protein in the outer membrane of bacteria from the family Enterobacteriaceae, can activate neutrophils and whether this activation is mediated by mechanisms that differ from those used by LPS or Escherichia coli diphosphoryl lipid A (EcDPLA). Neutrophil activation was assessed by measuring down-regulation of L-selectin and up-regulation of CD11b/CD18. When comparing molar concentrations of LP vs EcDPLA, LP was more potent (four times) at activating neutrophils. In contrast to LPS/EcDPLA, LP activation of neutrophils was serum independent. However, LP activation of neutrophils was enhanced by the addition of soluble CD14 and/or LPS-binding protein. In the presence of serum, LP activation of neutrophils was inhibited by different mAbs to CD14. This inhibition was significantly reduced or absent when performed in the absence of serum. Diphosphoryl lipid A from Rhodobacter spheroides (RaDPLA) completely inhibited LPS/EcDPLA activation of neutrophils but only slightly inhibited LP activation of neutrophils. These results suggest that LP activation of human neutrophils can be mediated by a mechanism that is different from LPS activation and that LP is a potentially important component in the development of diseases caused by Gram-negative bacteria of the family Enterobacteriaceae.

A laboratory simulation of toluene cleanup by air sparging of water-saturated sands

Laboratory air sparging experiments were performed in narrow acrylic tanks to evaluate the cleanup of toluene in water-saturated sands. Air flow channels in the sediment were identified by way of a colorimetric visualization technique, which allowed pore water samples to be collected at a known horizontal distance from an air channel. Pore water was sampled at periodic intervals during sparging experiments and analyzed by gas chromatography to yield toluene concentration vs. time data. Results indicate that channelized air flow is effective in reducing toluene concentrations in the range of 36-3 ppm, within 2 to 5 days, at least up to 185 mm from an active air channel. While relatively rapid, these toluene reduction times are longer than previously published data, from similar type experiments. The discrepancy is likely a function of air delivery flow rate and proximity of sampling sites to active air channels. Data from the current investigation were used to attempt an estimate of effective diffusion coefficients (D*) for toluene in clean, well-characterized sands in which the concentration gradient was imposed by sparge air. Calculated D* values range from 2. 98x10(-8) m(2)/s to 5.74x10(-9) m(2)/s, and are significantly faster than previously published values of toluene diffusion in clay soils. However, the values are also slightly greater than diffusion coefficients for toluene in aqueous solutions, indicating that the calculations more likely estimate coefficients of hydrodynamic dispersion (D(L)).

Adjuvant effects of cholera toxin b subunit on immune response to recombinant thyrotropin receptor in mice

We had previously shown that BALB/c mice immunized with the extracellular domain of human thyrotropin receptor (ETSHR) developed moderate hyperthyroxinemia. The antibody responses in these mice were predominantly of the IgG1 subclass. Since cholera toxin B subunit (CT-B) has direct effects on the thyroid, and is known to activate B lymphocytes and cause enhanced IgG1 production, we tested the ability of CT-B to modulate the antibody response to ETSHR. CT-B is unique in that it not only elicits a strong immune response to itself, but more importantly, when given with other antigens acts as a potent adjuvant. In the present study, BALB/c mice given ETSHR with CFA or CT-B via ip route showed higher titers of antibodies to ETSHR when compared to mice similarly immunized with ETSHR alone, or with IFA. Antibodies in ETSHR+CT-B immunized mice were mostly of the IgG1 subclass and reacted predominantly with ETSHR peptides 1 (aa 22-41), 21 (aa 322-341), and 23 (352-371). In contrast, animals immunized with ETSHR+CFA showed IgG1, IgG2a and IgG2b responses and reacted with peptides 1 and 21. Furthermore, mice immunized with ETSHR along with CT-B showed significantly higher levels of thyrotropin (TSH) binding inhibitory immunoglobulins (TBII) compared to those that did not receive CT-B. None of the mice immunized with a control antigen showed antibody response to ETSHR. These results suggested that CT-B could enhance and modulate immune response to ETSHR.

Thin and thick filament regulation of contractility in experimental cerebral vasospasm

OBJECTIVE

Cerebral vasospasm is a potentially fatal consequence of aneurysmal subarachnoid hemorrhage and influences the prognosis of the patient. The purpose of this study was to evaluate the status of thin (actin) and thick (myosin) filament regulation of smooth muscle contraction in the double-subarachnoid hemorrhage canine model of cerebral vasospasm and to determine the effects of a kinase inhibitor reported to be effective in vasospasm, HA1077, on thin and thick filament regulation.

METHODS

Cerebral vasospasm was assessed by vertebral angiography. Myosin regulatory light chain phosphorylation was measured using glycerol-urea gels, whereas protein levels of the thin filament-associated protein calponin were measured by Western blot.

RESULTS

The basilar arteries of dogs in which subarachnoid hemorrhage was induced narrowed to 36% +/- 2.0% of their size on the first day (n = 12). The phosphorylation of the regulatory light chain tended to increase, but the change did not reach statistical significance (35% +/- 5.9% [n = 12] versus 25% +/- 4.8% [n = 10] in control arteries). In contrast to this increase, significant degradation of calponin was observed in the samples from vasospastic dogs (85.4% +/- 5.45% [n = 5] versus 15.2% +/- 6.21% [n = 5]; P < 0.01). Prophylactic treatment with intravenous injections of HA1077 at 0.67 mg/kg b.i.d. significantly inhibited vasospasm (diameters, 65% +/- 10.2% of Day 1 diameters [n = 5]; P < 0.05), and calponin degradation (57.8% +/- 13.9% [n = 4]) was substantially reduced.

CONCLUSION

These data suggest that degradation of the thin filament-associated protein calponin plays a role in cerebral vasospasm and that the antivasospastic action of HA1077 is, at least in part, due to prevention of calponin degradation.

Melittin activates endogenous phospholipase D during cytolysis of human monocytic leukemia cells

Human monocytic leukemia cells (U937) were challenged with synthetic melittin, and arachidonic acid (AA)/acylated lipids from both cells (pellet) and media (supernatant) were analyzed by thin layer chromatography (TLC). From these data, melittin-mediated activation/inhibition of major phospholipases in U937 cells was related to pore formation, permeabilization and cytolysis as determined by light microscopy. Also, the effect of melittin on acylhydrolase activity in the cell-free sonicated lysates of U937 cells was examined. Here we report that synthetic melittin (1 microM) caused cytolysis of U937 cells within 10-15 min. Cellular hypertrophy (5 min) and aggregation (1 min) preceded cytolysis. TLC analysis of these lipids showed that total levels (cellular + medium) of diacylglycerol (DAG), phosphatidylethanolamine (PE) and phosphatidylcholine (PC) decreased, while that of arachidonic acid (AA) increased continuously (5-30 min). However, levels of phosphatidylethanol (PEt) phosphatidic acid (PA) and phosphatidylserine (PS) were increased transiently at 5-10 min being maximal at 5 min. Taken together, the combined levels of PEt and PA (an end product of phopholipase D, PLD) were about 42-fold higher than the level of AA at 5-10 min. Enhancement of AA levels appeared to result from in vitro reactions of various acylhydrolases and their phospholipid substrates (free/membrane bound) liberated into the medium during pore formation/cell lysis. Incubation of sonicated cell lysates also enhanced release of AA, which decreased upon addition of melittin, indicating that melittin inhibited these acylhydrolases. A consistent decrease in the level of DAG showed that phospholipase C was unaffected. Hence, transient activation of PLD bymelittin at the point of initiation of cytolysis, suggested a role for PLD in melittin-mediated membrane disruption/cytolysis by an uncharacterized signal transduction mechanism.

Surveillance of suicidal behavior in Kitsap County, Washington: a retrospective study

Suicide is a major source of preventable morbidity and mortality in Kitsap County, Washington State. This article describes a study of suicidal behavior to identify risk groups in order to design intervention strategies. A retrospective study was conducted by reviewing the charts of individuals exhibiting suicidal behavior who had presented to the county's only civilian hospital emergency department over a 7 month period. Frequencies were calculated to identify at-risk populations and determine risk factors. One hundred forty-five charts were reviewed. Subjects were mostly female (69%), and ages ranged from 10 to 80 years with 73% between 15 and 44 years. Two-thirds of the subjects were not working. More than half had previously exhibited suicidal behavior and more than 75% had previous mental health encounter(s). Most admissions (67.6%) occurred between 4:00 p.m. and 4:00 a.m. The core public health functions of assessment, policy development, and assurance provided the framework for this community to explore the finding that suicide was a major source of preventable morbidity and mortality. Community-based intervention strategies have been developed in an effort to reach the Healthy People 2000 objective of reducing suicide deaths to no more than 10.5 per 100,000 residents.

Role of Salmonella enterotoxin in overall virulence of the organism

In this study, the Salmonella enterotoxin gene (stn) was mutated by marker exchange mutagenesis, and the overall virulence of the organism was evaluated. Salmonella marker exchange mutants evoked significantly less fluid secretion in mouse intestinal loops compared to that seen with wild-type S. typhimurium. Salmonella mutants were as invasive as wild-type bacteria for HeLa cells; however, their capacity to cause destruction of the intestinal mucosa was impaired, when compared with wild-type bacteria by electron microscopy. Upon oral challenge of mice, the LD(50)of the Salmonella mutants was greater than that for the wild-type bacteria. The fluid secretory potential, as well as a reduction in the LD(50)of these mutants was restored when the mutated stn gene was replaced by the native stn gene sequence. These mutations had no effect on the aerobic growth of these bacteria in minimal or complete medium; anaerobic growth was also not affected. With these studies, we demonstrated that the presence of an intact stn gene contributed significantly to the overall virulence of S. typhimurium in a murine model.

Cholera toxin B subunit activates arachidonic acid metabolism

Cholera toxin (CT) increases intestinal secretion of water and electrolytes and modulates the mucosal immune response by stimulating cellular synthesis of arachidonic acid (AA) metabolites (e.g., prostaglandin E2), as well as the intracellular second messenger cyclic AMP (cAMP). While much is known about the mechanism of CT stimulation of adenylate cyclase, the toxin's activation of phospholipase A2, which results in increased hydrolysis of AA from membrane phospholipids, is not well understood. To determine whether CT activation of AA metabolism requires CT's known enzymatic activity (i.e., ADP-ribosylation of GSalpha), we used native CT and a mutant CT protein (CT-2*) lacking ADP-ribose transferase activity in combination with S49 wild-type (WT) and S49 cyc- murine Theta (Th)1.2-positive lymphoma cells deficient in GSalpha. The experimental results showed that native CT stimulated the release of [3H[AA from S49 cyc- cells at a level similar to that for S49 WT cells, indicating that GSalpha is not essential for this process. Further, levels of cAMP in the CT-treated cyc- cells remained the same as those in the untreated control cells. The ADP-ribosyltransferase-deficient CT-2* protein, which was incapable of increasing synthesis of cAMP, displayed about the same capacity as CT to evoke the release of [3H]AA metabolites from both S49 WT and cyc- cells. We concluded that stimulation of arachidonate metabolism in S49 murine lymphoma cells by native CT does not require enzymatically functional CT, capable of catalyzing the ADP-ribosylation reaction. These results demonstrated for the first time that stimulation of adenylate cyclase by CT and stimulation of AA metabolism by CT are not necessarily coregulated. In addition, the B subunits purified from native CT and CT-2* both simulated the release of [3H]AA from S49 cyc- cells and murine monocyte/macrophage cells (RAW 264.7), suggesting a receptor-mediated cell activation process of potential importance in enhancing immune responses to vaccine components.

Molecular characterization of cDNA for phospholipase A2-activating protein

A phospholipase A2-activating protein (PLAP) cDNA was cloned and sequenced from a human monocyte cDNA library, and expressed as a histidine-tagged fusion protein. The DNA-deduced aa sequence of human PLAP was 80,826 Da; however, SDS-PAGE analysis revealed a 72-74 kDa protein which matched the size of native PLAP from human monocytes. Anti-sense plap oligonucleotide blocked cholera toxin-induced release of 3H-labeled arachidonic acid from cells, indicating a potential role for PLAP in regulating phospholipase A2 activity.

Antisera to selected outer membrane proteins of Vibrio cholerae protect against challenge with homologous and heterologous strains of V. cholerae

Each year cholera epidemics occur in various places around the world. Though there is no effective vaccine against cholera, people who recover from an infection usually have prolonged immunity to the disease. Sera from convalescent patients contain antibodies to a number of outer membrane proteins (OMPs) of V. cholerae. We isolated several OMPs (43, 42, 30, and 22 kDa) from V. cholerae V86 E1 Tor Inaba, sequenced their amino-termini, and generated hyperimmune sera against them in rabbits. Antisera to the 43-, 42-, and 22-kDa OMPs, but not the preimmune sera, significantly reduced V. cholerae-induced fluid secretion seen in rabbit intestinal loops challenged with the homologous strain. In addition, a combination of antisera to the different OMPs reduced the fluid secretion induced by challenge with heterologous V. cholerae Ogawa and O139 strains. These results have significance in the development of vaccines to V. cholerae, as the hyperexpression of these OMP encoding genes in vaccine strains may improve the efficacy of cholera vaccines.

Lipoprotein release by bacteria: potential factor in bacterial pathogenesis

Lipoprotein (LP) is a major component of the outer membrane of bacteria in the family Enterobacteriaceae. LP induces proinflammatory cytokine production in macrophages and lethal shock in LPS-responsive and -nonresponsive mice. In this study, the release of LP from growing bacteria was investigated by immuno-dot blot analysis. An immuno-dot blot assay that could detect LP at levels as low as 100 ng/ml was developed. By using this assay, significant levels of LP were detected in culture supernatants of growing Escherichia coli cells. During mid-logarithmic growth, approximately 1 to 1.5 microgram of LP per ml was detected in culture supernatants from E. coli. In contrast, these culture supernatants contained 5 to 6 microgram/ml of lipopolysaccharide (LPS). LP release was not unique to E. coli. Salmonella typhimurium, Yersinia enterocolitica, and two pathogenic E. coli strains also released LP during in vitro growth. Treatment of bacteria with the antibiotic ceftazidime significantly enhanced LP release. Culture supernatants from 5-h cultures of E. coli were shown to induce in vitro production of interleukin-6 (IL-6) by macrophages obtained from LPS-nonresponsive C3H/HeJ mice. In contrast, culture supernatants from an E. coli LP-deletion mutant were significantly less efficient at inducing IL-6 production in C3H/HeJ macrophages. These results suggest, for the first time, that LP is released from growing bacteria and that this released LP may play an important role in the induction of cytokine production and pathologic changes associated with gram-negative bacterial infections.

Protection against exotoxin A (ETA) and Pseudomonas aeruginosa infection in mice with ETA-specific antipeptide antibodies

Pseudomonas aeruginosa is an opportunistic pathogen that causes serious and sometimes fatal infections in the compromised host, especially in patients with major trauma or thermal injuries. Exotoxin A (ETA) is the major and most lethal virulence factor produced by this ubiquitous microorganism. In a recent study (H. S. Elzaim, A. K. Chopra, J. W. Peterson, R. Goodheart, and J. P. Heggers, Infect. Immun. 66:2170-2179, 1998), we identified two major epitopes, one within the translocation domain (amino acid [aa] residues 289 to 333) of ETA and another within the enzymatic domain (aa 610 to 638), by using a panel of antipeptide antibodies. Synthetic peptides representing these two epitopes induced ETA-specific antibodies which were able to abrogate the cytotoxic activity of ETA, as measured by incorporation of [3H]leucine into 3T3 fibroblasts. In the present study, these antibodies were tested for the ability to provide protection against ETA and infection with a toxin-producing strain of P. aeruginosa in a mouse model. Antibodies to either of the synthetic peptides conferred protection against ETA. Also, when used for immunization, both peptides induced active immunity to ETA in mice. Antibodies to the peptide representing a region within the enzymatic domain of ETA, in combination with the antibiotic amikacin, enhanced the survival of mice infected with a toxin-producing strain of P. aeruginosa. Thus, antipeptide antibodies specific for ETA might be paired with antibiotic treatment for passive immunization of patients suffering from P. aeruginosa infection.

Cloning, sequencing and expression of the flagellin core protein and other genes encoding structural proteins of the Vibrio cholerae flagellum

Vibrio cholerae is a Gram-negative bacterium with a single polar flagellum. Motility is an important virulence factor for this non-invasive pathogen. We cloned and sequenced a locus in V. cholerae V86 (El Tor, Inaba) that contained five different structural genes of the flagellum. The cloned genes and their products were assigned names and functions based on homology with sequences of similar genes and their products from other related bacteria. All of these genes of V. cholerae V86, namely, flgI, J, M, L and flaA, were transcribed in the same direction. These genes respectively encoded the P- and L-ring proteins, the hook-associated proteins 1 and 3 and the flagellin core protein of the flagellum. Our data indicated the presence of more than one flagellar locus in V. cholerae which could provide a means of immunoavoidance during infection. When compared with homologs in other bacteria, the flagellin core protein of V. cholerae exhibited conservation in the N- and C-termini, but had diverged in the central region.

Role of a cytotoxic enterotoxin in Aeromonas-mediated infections: development of transposon and isogenic mutants

Transposon and marker exchange mutagenesis were used to evaluate the role of Aeromonas cytotoxic enterotoxin (Act) in the pathogenesis of diarrheal diseases and deep wound infections. The transposon mutants were generated by random insertion of Tn5-751 in the chromosomal DNA of a diarrheal isolate SSU of Aeromonas hydrophila. Some of the transposon mutants had dramatically reduced hemolytic and cytotoxic activities, and such mutants exhibited reduced virulence in mice compared to wild-type Aeromonas when injected intraperitoneally (i.p.). Southern blot data indicated that transposition in these mutants did not occur within the cytotoxic enterotoxin gene (act). The transcription of the act gene was affected drastically in the transposon mutants, as revealed by Northern blot analysis. The altered virulence of these transposon mutants was confirmed by developing isogenic mutants of the wild-type Aeromonas by using a suicide vector. In these mutants, the truncated act gene was integrated in place of a functionally active act gene. The culture filtrates from isogenic mutants were devoid of hemolytic, cytotoxic, and enterotoxic activities associated with Act. These filtrates caused no damage to mouse small intestinal epithelium, as determined by electron microscopy, whereas culture filtrates from wild-type Aeromonas caused complete destruction of the microvilli. The 50% lethal dose of these mutants in mice was 1.0 x 10(8) when injected i. p., compared to 3.0 x 10(5) for the wild-type Aeromonas. Reintegration of the native act gene in place of the truncated toxin gene in isogenic mutants resulted in complete restoration of Act's biological activity and virulence in mice. The animals injected with a sublethal dose of wild-type Aeromonas or the revertant, but not the isogenic mutant, had circulating toxin-specific neutralizing antibodies. Taken together, these studies clearly established a role for Act in the pathogenesis of Aeromonas-mediated infections.

Education of advanced practice nurses. Serving vulnerable populations

Vulnerable populations are camouflaged, stigmatized, and often lacking in health care services. They may also be distrustful of assistance from traditional health care providers. To better serve vulnerable populations, professionals guiding intervention programs need specialized knowledge and skills as well as problem-solving abilities.

Generation of neutralizing antipeptide antibodies to the enzymatic domain of Pseudomonas aeruginosa exotoxin A

Burn patients suffer a break in the physical barrier (skin), which, when combined with their generalized state of immunodeficiency, creates an open window for opportunistic infections, mainly with Pseudomonas aeruginosa. Infection of the burn wound has always been a major factor in retardation of wound healing, and sepsis remains the leading cause of death in burn patients. Because studies have shown that topical treatment with antiexotoxin A (ETA) antibodies significantly increases survival in rats infected with toxin-producing strains of P. aeruginosa, we examined 11 synthetic peptides encompassing 12 to 45 amino acid (aa) residues, representing what were predicted by computer analysis to be the most hydrophilic and antigenic regions of ETA. These synthetic peptides were injected into rabbits for antibody production. Different groups of rabbits were immunized with a combination of peptides, with each combination representing one of the three distinct domains of ETA. Animals immunized with various peptide combinations produced peptide-specific antibodies that exhibited cross-reactivity to ETA. Two major epitopes were identified on the ETA molecule by experiments with peptide-specific antibodies in enzyme-linked immunosorbent assay and immunoprecipitation. One of these epitopes was located in the translocation domain (II) (aa 297 to 310), while the other was mapped to the last 13 aa residues at the carboxy-terminal end of the enzymatic domain (III) (aa 626 to 638). Of these two regions, the epitope in the enzymatic domain induced a much higher level of neutralizing antibodies that abrogated the cytotoxic activity of ETA in vitro. Antibodies to this epitope blocked the ADP-ribosyltransferase activity of ETA and appeared to interfere with binding of the substrate elongation factor 2 to the enzymatic active site of the ETA molecule. We conclude that polyclonal, as well as monoclonal, antibodies to short peptides, representing small regions of ETA, may have therapeutic potential in passive immunization or topical treatment of burn patients infected with toxin-producing strains of P. aeruginosa.

Anti-inflammatory and antisecretory potential of histidine in Salmonella-challenged mouse small intestine

Challenge of mouse small intestinal loops with Salmonella typhimurium invoked the accumulation of luminal fluid, acute inflammation, and extensive structural damage to the small intestinal mucosa, as determined by histology and electron microscopy. Intraperitoneal and intestinal luminal injection of L-histidine, a known antioxidant, reduced the amount of fluid accumulating in the intestinal lumen and protected the intestinal tissue from S. typhimurium-induced damage. The reduction in S. typhimurium-induced fluid accumulation by L-histidine was specific for the L-enantiomer because D-histidine had no significant protective effect. Efficacy of L-histidine in protecting the infected intestinal tissue was attributed to the capacity of the imidazole ring to scavenge reactive oxygen species (ROS) generated by cells in the intestine during the acute inflammatory response. Glutathione levels were markedly reduced in S. typhimurium-challenged, inflamed intestinal tissues as a result of ROS generation. Importantly, after dosing the S. typhimurium-challenged mice with L-histidine, the glutathione content of the small intestinal tissue was not significantly different from mock-challenged controls. Further evidence favoring this mechanism included the capacity of L-histidine to scavenge ROS produced as a result of lipopolysaccharide (LPS) exposure of mononuclear cells (U937), as demonstrated with a redox-sensitive fluorescent dye (2'7'-dichlorodihydrofluorescein [DCF]). Addition of L-histidine, and to a lesser extent D-histidine, to the culture media of U937 cells before LPS exposure, resulted in a significant dose-dependent reduction in LPS-induced intracellular DCF fluorescence, as measured quantitatively by flow cytometry. The potential therapeutic value of anti-inflammatory drugs containing an L-histidine-like structure could protect infected mucosal tissues irrespective of microbial etiology.

Augmentation of both hemolysate-induced contraction and activation of protein kinase C by submaximum activation in canine cerebral arteries in vitro

Although phorbol esters, synthetic activators of protein kinase C (PKC), can stimulate large increases in the binding of cytosolic PKC to form membrane-bound PKC (PKCm, an indicator of PKC activation), the authors report that even small increases in PKCm induced by phorbol esters (8-12% of total PKC content) can be associated with significant PKC-mediated contractions in vitro (50-85% of maximum) in normal canine cerebral arteries. Increases in PKCm of similarly small magnitude were found in vitro when control artery segments were exposed to hemolysate, but only if the arterial smooth-muscle cells were first slightly depolarized by increased extracellular potassium to values of membrane potential similar to those observed in canine cerebral arteries during chronic cerebral vasospasm. These increases in PKCm (6-8% of total PKC content) coincided with a greatly augmented contractile response to hemolysate. These results show that the previous observation of only a small increase in PKCm (approximately 7% of total PKC content) after experimental subarachnoid hemorrhage in the canine model does not preclude a potentially important role for PKC-mediated contraction in the pathogenesis of cerebral vasospasm.