Acute and two-week inhalation toxicity studies in rats for Polyalphaolefin (PAO) fluid.

Formal occupational exposure limits (OELs) for polyalphaolefin (PAO) fluids have not been proposed. Specific PAO fluids are utilized as aircraft hydraulics or heat sink coolants for electronics and aircraft service air. Toxicity was compared for a PAO fluid in male and female Fischer 344 rats using acute inhalation (0, 100, 500, or 1000 mg/m3 aerosol for 6 hr) and two-week inhalation (0, 20, 100, or 300 mg/m3 aerosol for 6 hr/day, 5 days/week) studies. Neurobehavioral tests following acute exposure showed that both genders were less responsive after exposure to 1000 mg/m3 PAO, and to a lesser extent following 500 mg/m3 PAO. Body weight, food, and water consumption were also affected with recovery after 24 hr. Histopathology for the acute group demonstrated an exposure response increase in severity (minimal to mild) of lesions in the posterior nasal cavities and lungs. Severity of lesions was reduced in the recovery groups (normal to minimal). Acute effects were short-lived and recoverable. Following the two-week exposure, effects were limited to lesions only in the posterior nasal cavities and lungs of the high exposure group, with less severity than in the acute exposure high concentration group. Short-term repeated exposure did not result in any cumulative effects except for minimal respiratory tract changes in the 300 mg/m3 exposure group. Data-driven operational exposure limits (OpELs) were proposed based upon Acute Exposure Guideline Levels process resulting in values of 28, 28, 14, 3.5, and 1.7 mg/m3 for 10 and 30 min, 1, 4, and 8 hr, respectively.

Toxicity and human health assessment of an alcohol-to-jet (ATJ) synthetic kerosene.

A toxicological investigation was conducted for alcohol-to-jet (ATJ) fuels intended as a 50:50 blend with petroleum-derived fuel Jet Propulsion (JP)-8. The ATJ synthetic paraffinic kerosene (SPK) fuel was produced by Gevo (Englewood CO) and derived either from biomass (bio) or non-biomass sources. All toxicity tests were performed with one or both ATJ fuels following addition of a standard additive package required for JP-8. The primary fuel, Gevo (bio) ATJ SPK produced from biomass-derived iso-butanol, exhibited the same dermal irritation potential in rabbits as JP-8; the non-biomass-derived fuel was less irritating. The Gevo (bio) fuel was non-clastogenic in micronucleus testing with rats and neither version was mutagenic in the bacterial reverse mutation assay. A 90-day study was performed with Gevo (bio) ATJ SPK by exposing male and female Fischer 344 rats to target concentrations of 0, 200, 700 or 2000 mg/m3 of fuel, 6 hr per day, 5 days a week for 69 exposure days and included neurobehavioral assays and reproductive health evaluations in the study design. Results were negative or limited to irritant effects in the respiratory system due to exposure to a vapor and aerosol mixture in the 2000 mg/m3 exposure group. Occupational exposure limits for JP-8 were proposed for these ATJ fuels since these fuels display similar or somewhat lower toxicity than JP-8. As both versions of the Gevo ATJ jet fuel were similar, handling of either fuel alone or in a blend with petroleum-derived JP-8 appears unlikely to increase human health risks for workers.

Toxicity and occupational exposure assessment for hydroprocessed esters and fatty acids (HEFA) alternative jet fuels.

The U.S. Air Force (USAF) has pursued development of alternative fuels to augment or replace petroleum-based jet fuels. Hydroprocessed esters and fatty acids (HEFA) renewable jet fuel is certified for use in commercial and USAF aircraft. HEFA feedstocks include camelina seed oil (Camelina sativa, HEFA-C); rendered animal fat (tallow, HEFA-T); and mixed fats and oils (HEFA-F). The aim of this study was to examine potential toxic effects associated with HEFA fuels exposures. All 3 HEFA fuels were less dermally irritating to rabbits than petroleum-derived JP-8 currently in use. Inhalation studies using male and female Fischer-344 rats included acute (1 day, with and without an 11-day recovery), 5-, 10- or 90-day durations. Rats were exposed to 0, 200, 700 or 2000 mg/m3 HEFA-F (6 hr/day, 5 days/week). Acute, 5 - and 10-day responses included minor urinalysis effects. Kidney weight increases might be attributed to male rat specific hyaline droplet formation. Nasal cavity changes included olfactory epithelial degeneration at 2000 mg/m3. Alveolar inflammation was observed at ≥700 mg/m3. For the 90-day study using HEFA-C, no significant neurobehavioral effects were detected. Minimal histopathological effects at 2000 mg/m3 included nasal epithelium goblet cell hyperplasia and olfactory epithelium degeneration. A concurrent micronucleus test was negative for evidence of genotoxicity. All HEFA fuels were negative for mutagenicity (Ames test). Sensory irritation (RD50) values were determined to be 9578 mg/m3 for HEFA-C and greater than 10,000 mg/m3 for HEFA-T and HEFA-F in male Swiss-Webster mice. Overall, HEFA jet fuel was less toxic than JP-8. Occupational exposure levels of 200 mg/m3 for vapor and 5 mg/m3 for aerosol are recommended for HEFA-based jet fuels.

Comparative electrophysiological evaluation of hippocampal function following repeated inhalation exposures to JP-8, Jet A, JP-5, and the synthetic Fischer Tropsch fuel.

Exposure to fuels continues to be a concern in both military and general populations. The aim of this study was to examine effects of in vivo rat repeated exposures to different types of jet fuel utilizing microelectrode arrays for comparative electrophysiological (EP) measurements in hippocampal slices. Animals were exposed to increasing concentrations of four jet fuels, Jet Propellant (JP)-8, Jet A, JP-5, or synthetic Fischer Tropsch (FT) fuel via whole-body inhalation for 20 d (6 hr/d, 5 d/week for 28 d) and synaptic transmission as well as behavioral performance were assessed. Our behavioral studies indicated no significant changes in behavioral performance in animals exposed to JP-8, Jet A, or JP-5. A significant deviation in learning pattern during the Morris water maze task was observed in rats exposed to the highest concentration of FT (2000 mg/m3). There were also significant differences in the EP profile of hippocampal neurons from animals exposed to JP-8, Jet A, JP-5, or FT compared to control air. However, these differences were not consistent across fuels or dose dependent. As expected, patterns of EP alterations in brain slices from JP-8 and Jet A exposures were more similar compared to those from JP-5 and FT. Further longitudinal investigations are needed to determine if these EP effects are transient or persistent. Such studies may dictate if and how one may use EP measurements to indicate potential susceptibility to neurological impairments, particularly those that result from inhalation exposure to chemicals or mixtures.

Indications of Endocrine Disruptor Effects of JP-5 Jet Fuel Using a Rat-Model Reproductive Study and an In Vitro Human Hormone Receptor Assay.

Recent events concerning jet fuel contamination of drinking water have shown that we need a better understanding of the effects of ingested jet fuel. To this end, a reproductive study with ingested jet fuel in rats was undertaken with relatively high concentrations of Jet Propellant (JP)-5 along with a human estrogen receptor activation in vitro assay using JP-5, JP-8, and an alternative jet fuel derived from the camelina plant referred to as HydroRenewable Jet (HRJ) fuel, to help evaluate potential effects of ingested jet fuel. The results of the in vivo study provide evidence that JP-5 can act as an endocrine disruptor, with specific observations including altered hormone levels with JP-5 exposure (significantly lower estradiol levels in male rats and significantly increased Dehydroepiandrosterone levels in females), and a decreased male/female offspring ratio. The in vitro hormone receptor activation assay indicated that JP-5 and JP-8 are capable of upregulating human estrogen receptor (ER) activity, while HRJ was not active in the ER assay. The jet fuels were not able to activate androgen or glucocorticoid receptors in further in vitro assays. These results infer potential endocrine disruption associated with JP-5, with activation of the estrogen receptor as one potential mechanism of action.

The ERM protein, ezrin, regulates neutrophil transmigration by modulating the apical localization of MRP2 in response to the SipA effector protein during Salmonella Typhimurium infection.

In human disease induced by Salmonella enterica serovar Typhimurium (S. Typhimurium), transepithelial migration of neutrophils rapidly follows attachment of the bacteria to the epithelial apical membrane. We have previously shown that during S. Typhimurium infection the multidrug resistance-associated protein 2 (MRP2) is highly expressed at the apical surface of the intestinal epithelia, and that it functions as an efflux pump for the potent neutrophil chemoattractant hepoxilin A(3) . However, the molecular mechanisms regulating its apical localization during active states of inflammation remain unknown. Thus, our objective was to determine the mechanistic basis for the translocation of MRP2 to the apical surface of intestinal epithelial cells during S. Typhimurium infection. We show that suppression of ezrin, through either RNAi or truncation of the C-terminus, results not only in a decrease in S. Typhimurium-induced neutrophil transmigration but also significantly attenuates the apical membrane expression of MRP2 during Salmonella infection. In addition, we determined that S. Typhimurium induces the activation of ezrin via a PKC-α-dependent pathway and that ezrin activation is coupled to apical localization of MRP2. Based on these results we propose that activation of ezrin is required for the apical localization of MRP2 during S. Typhimurium infection.

Selective eicosanoid-generating capacity of cytoplasmic phospholipase A2 in Pseudomonas aeruginosa-infected epithelial cells.

Airway neutrophil infiltration is a pathological hallmark observed in multiple lung diseases including pneumonia and cystic fibrosis. Bacterial pathogens such as Pseudomonas aeruginosa instigate neutrophil recruitment to the air space. Excessive accumulation of neutrophils in the lung often contributes to tissue destruction. Previous studies have unveiled hepoxilin A(3) as the key molecular signal driving neutrophils across epithelial barriers. The eicosanoid hepoxilin A(3) is a potent neutrophil chemoattractant produced by epithelial cells in response to infection with P. aeruginosa. The enzyme phospholipase A(2) liberates arachidonic acid from membrane phospholipids, the rate-limiting step in the synthesis of all eicosanoids, including hepoxilin A(3). Once generated, aracidonic acid is acted upon by multiple cyclooxygenases and lipoxygenases producing an array of functionally diverse eicosanoids. Although there are numerous phospholipase A(2) isoforms capable of generating arachidonic acid, the isoform most often associated with eicosanoid generation is cytoplasmic phospholipase A(2)α. In the current study, we observed that the cytoplasmic phospholipase A(2)α isoform is required for mediating P. aeruginosa-induced production of certain eicosanoids such as prostaglandin E(2). However, we found that neutrophil transepithelial migration induced by P. aeruginosa does not require cytoplasmic phospholipase A(2)α. Furthermore, P. aeruginosa-induced hepoxilin A(3) production persists despite cytoplasmic phospholipase A(2)α suppression and generation of the 12-lipoxygenase metabolite 12-HETE is actually enhanced in this context. These results suggest that alterative phospholipase A(2) isoforms are utilized to synthesize 12-lipoxygenase metabolites. The therapeutic implications of these findings are significant when considering anti-inflammatory therapies based on targeting eicosanoid synthesis pathways.

Shigella flexneri type III secretion system effectors OspB and OspF target the nucleus to downregulate the host inflammatory response via interactions with retinoblastoma protein.

OspF, OspG and IpaH(9.8) are type III secretion system (T3SS) effectors of Shigella flexneri that downregulate the host innate immune response. OspF modifies mitogen-activated protein kinase pathways and polymorphonuclear leucocyte transepithelial migration associated with Shigella invasion. OspF also localizes in the nucleus to mediate chromatin remodelling, resulting in reduced transcription of inflammatory cytokines. We now report that OspB can be added to the set of S. flexneri T3SS effectors required to modulate the innate immune response. T84 cells infected with a Delta ospB mutant resulted in reduced polymorphonuclear leucocyte transepithelial migration and mitogen-activated protein kinase signalling. Tagged versions of OspB localized with endosomes and the nucleus. Further, T84 cells infected with the Delta ospB mutant showed increased levels of secreted IL-8 compared with wild-type infected cells. Both GST-OspB and GST-OspF coprecipitated retinoblastoma protein from host cell lysates. Because Delta ospB and Delta ospF mutants share similar phenotypes, and OspB and OspF share a host binding partner, we propose that OspB and OspF facilitate the remodelling of chromatin via interactions with retinoblastoma protein, resulting in diminished inflammatory cytokine production. The requirement of multiple T3SS effectors to modulate the innate immune response correlates to the complexity of the human immune system.

Multidrug resistance-associated transporter 2 regulates mucosal inflammation by facilitating the synthesis of hepoxilin A3.

Neutrophil transmigration across mucosal surfaces contributes to dysfunction of epithelial barrier properties, a characteristic underlying many mucosal inflammatory diseases. Thus, insight into the directional movement of neutrophils across epithelial barriers will provide important information relating to the mechanisms of such inflammatory disorders. The eicosanoid hepoxilin A(3), an endogenous product of 12-lipoxygenase activity, is secreted from the apical surface of the epithelial barrier and establishes a chemotactic gradient to guide neutrophils from the submucosa across epithelia to the luminal site of an inflammatory stimulus, the final step in neutrophil recruitment. Currently, little is known regarding how hepoxilin A(3) is secreted from the intestinal epithelium during an inflammatory insult. In this study, we reveal that hepoxilin A(3) is a substrate for the apical efflux ATP-binding protein transporter multidrug resistance-associated protein 2 (MRP2). Moreover, using multiple in vitro and in vivo models, we show that induction of intestinal inflammation profoundly up-regulates apical expression of MRP2, and that interfering with hepoxilin A(3) synthesis and/or inhibition of MRP2 function results in a marked reduction in inflammation and severity of disease. Lastly, examination of inflamed intestinal epithelia in human biopsies revealed up-regulation of MRP2. Thus, blocking hepoxilin A(3) synthesis and/or inhibiting MRP2 may lead to the development of new therapeutic strategies for the treatment of epithelial-associated inflammatory conditions.

Evaluation of Probiotics for Warfighter Health and Performance.

The probiotic industry continues to grow in both usage and the diversity of products available. Scientific evidence supports clinical use of some probiotic strains for certain gastrointestinal indications. Although much less is known about the impact of probiotics in healthy populations, there is increasing consumer and scientific interest in using probiotics to promote physical and psychological health and performance. Military men and women are a unique healthy population that must maintain physical and psychological health in order to ensure mission success. In this narrative review, we examine the evidence regarding probiotics and candidate probiotics for physical and/or cognitive benefits in healthy adults within the context of potential applications for military personnel. The reviewed evidence suggests potential for certain strains to induce biophysiological changes that may offer physical and/or cognitive health and performance benefits in military populations. However, many knowledge gaps exist, effects on health and performance are generally not widespread among the strains examined, and beneficial findings are generally limited to single studies with small sample sizes. Multiple studies with the same strains and using similar endpoints are needed before definitive recommendations for use can be made. We conclude that, at present, there is not compelling scientific evidence to support the use of any particular probiotic(s) to promote physical or psychological performance in healthy military personnel. However, plausibility for physical and psychological health and performance benefits remains, and additional research is warranted. In particular, research in military cohorts would aid in assessing the value of probiotics for supporting physical and psychological health and performance under the unique demands required of these populations.

The NleE/OspZ family of effector proteins is required for polymorphonuclear transepithelial migration, a characteristic shared by enteropathogenic Escherichia coli and Shigella flexneri infections.

Enteropathogenic Escherichia coli (EPEC) and Shigella flexneri are human host-specific pathogens that infect intestinal epithelial cells. However, each bacterial species employs a different infection strategy within this environmental niche. EPEC attaches to the apical surface of small intestine enterocytes, causing microvillus effacement and rearrangement of the host cell cytoskeleton beneath adherent bacteria. In contrast, S. flexneri invades the large intestine epithelium at the basolateral membrane, replicates, and spreads cell to cell. Both EPEC and S. flexneri rely on type three secretion systems (T3SS) to secrete effectors into host cells, and both pathogens recruit polymorphonuclear leukocytes (PMNs) from the submucosa to the lumen of the intestine. In this report, we compared the virulence functions of the EPEC T3SS effector NleE and the homologous Shigella protein Orf212. We discovered that Orf212 was secreted by the S. flexneri T3SS and renamed this protein OspZ. Infection of polarized T84 intestinal epithelial cells with an ospZ deletion mutant of S. flexneri resulted in reduced PMN transepithelial migration compared to infection by the wild type. An nleE deletion mutant of EPEC showed a similar reduction of PMN migration. The ability to induce PMN migration was restored in both mutants when either ospZ or nleE was expressed from a plasmid. An infection of T84 cells with the delta ospZ mutant resulted in reduced extracellular signal-related kinase phosphorylation and NF-kappaB activation compared to infection with the wild type. Therefore, we conclude that OspZ and NleE have similar roles in the upstream induction of host signaling pathways required for PMN transepithelial migration in Shigella and EPEC infections.

Distinct isoforms of phospholipase A2 mediate the ability of Salmonella enterica serotype typhimurium and Shigella flexneri to induce the transepithelial migration of neutrophils.

Salmonella spp. and Shigella spp. are responsible for millions of cases of enteric disease each year worldwide. While these pathogens have evolved distinct strategies for interacting with the human intestinal epithelium, they both induce significant proinflammatory responses that result in massive transepithelial migration of neutrophils across the intestinal mucosa. It has previously been shown with Salmonella enterica serotype Typhimurium that the process of neutrophil transmigration is mediated in part by the secretion of hepoxilin A(3) (HXA(3); 8-hydroxy-11,12-epoxy-eicosatetraenoic acid), a potent neutrophil chemoattractant, from the apical surface of infected model intestinal epithelium. This study confirms that HXA(3) is also secreted in response to infection by Shigella flexneri, that it is produced by a pathway involving 12/15-lipoxygenase (12/15-LOX), and that S. enterica serovar Typhimurium and S. flexneri share certain elements in the mechanism(s) that underlies the otherwise separate signal transduction pathways that are engaged to induce polymorphonuclear leukocyte (PMN) transepithelial migration (protein kinase C and extracellular signal-regulated kinases 1 and 2, respectively). PMN transepithelial migration in response to infection with S. flexneri was dependent on 12/15-LOX activity, the enzyme responsible for the initial metabolism of arachidonic acid to HXA(3). Probing further into this pathway, we also found that S. enterica serovar Typhimurium and S. flexneri activate different subtypes of phospholipase A(2), a critical enzyme involved in the liberation of arachidonic acid from cellular membranes. Thus, although S. enterica serovar Typhimurium and S. flexneri utilize different mechanisms for triggering the induction of PMN transepithelial migration, we found that their reliance on 12/15-LOX is conserved, suggesting that enteric pathogens may ultimately stimulate similar pathways for the synthesis and release of HXA(3).

Shigella depends on SepA to destabilize the intestinal epithelial integrity via cofilin activation.

Shigella is unique among enteric pathogens, as it invades colonic epithelia through the basolateral pole. Therefore, it has evolved the ability to breach the intestinal epithelial barrier to deploy an arsenal of effector proteins, which permits bacterial invasion and leads to a severe inflammatory response. However, the mechanisms used by Shigella to regulate epithelial barrier permeability remain unknown. To address this question, we used both an intestinal polarized model and a human ex-vivo model to further characterize the early events of host-bacteria interactions. Our results showed that secreted Serine Protease A (SepA), which belongs to the serine protease autotransporter of Enterobacteriaceae family, is responsible for critically disrupting the intestinal epithelial barrier. Such disruption facilitates bacterial transit to the basolateral pole of the epithelium, ultimately fostering the hallmarks of the disease pathology. SepA was found to cause a decrease in active LIM Kinase 1 (LIMK1) levels, a negative inhibitor of actin-remodeling proteins, namely cofilin. Correspondingly, we observed increased activation of cofilin, a major actin-polymerization factor known to control opening of tight junctions at the epithelial barrier. Furthermore, we resolved the crystal structure of SepA to elucidate its role on actin-dynamics and barrier disruption. The serine protease activity of SepA was found to be required for the regulatory effects on LIMK1 and cofilin, resulting in the disruption of the epithelial barrier during infection. Altogether, we demonstrate that SepA is indispensable for barrier disruption, ultimately facilitating Shigella transit to the basolateral pole where it effectively invades the epithelium.

Convenient determination of DNA extraction efficiency using an external DNA recovery standard and quantitative-competitive PCR.

Molecular biology techniques have advanced the field of microbial ecology through the analysis of nucleic acids. Most techniques that use DNA or RNA require their extraction from environmental matrices, which can be tedious and inefficient. While a number of extraction methods, both laboratory-based and commercially available, have been developed, none of these include a convenient method to determine extraction efficiency. We have developed an external DNA recovery standard, Lambda DNA (target DNA) contained within pBR322, allowing routine determinations of DNA recovery efficiency. Target DNA was added to sediments as whole cells, total DNA extracted using commercial DNA extraction/purification kits and the amount of target DNA recovered quantified by quantitative-competitive PCR (QC-PCR). Three commercially available kits (UltraClean Soil DNA, FastDNA SPIN and Soil Master DNA Extraction) were evaluated for recovery efficiency. Recoveries for the three kits ranged from undetectable to 43.3% with average recoveries of 14.9+/-16.0%, 28.3+/-10.5% and 2.4+/-0.1% (UltraClean, FastDNA and Soil Master, respectively). Quantification of target DNA proved robust in sediments heavily polluted with polycyclic aromatic hydrocarbons and the external recovery standard could be detected following extraction and amplification from as few as 1 x 10(3) cells added to 0.5 g sediment (wet weight). The external DNA recovery standard was also added directly to the sediment as purified plasmid DNA prior to extraction. It was recovered with similar efficiency as when added as whole cells, suggesting its usefulness in estimating DNA recovery in ribosomal DNA studies. These results show that, while the commercial kits offer expedited sample processing, the extraction efficiencies vary on a sample-by-sample basis and were <100%. Therefore, quantitative DNA studies require an estimation of DNA recovery.

The two-component sensor response regulator RoxS/RoxR plays a role in Pseudomonas aeruginosa interactions with airway epithelial cells.

Pseudomonas aeruginosa is an opportunistic pathogen that infects the lungs of patients with cystic fibrosis causing aberrant and destructive neutrophil (PMN)-dominated inflammation of airways. Interaction of P. aeruginosa with the lung epithelial barrier resulting in trans-epithelial PMN migration likely represents a key event during PMN recruitment. To investigate bacterial factors involved in interactions with lung epithelial cells, a mutant library of two-component system response regulators was evaluated to identify mutants exhibiting defects in the ability to induce PMN trans-epithelial migration. Of forty-eight mutants, five reproducibly demonstrated a reduced PMN trans-epithelial migration response. All five mutants also exhibited a decreased ability to interact with lung epithelial cells. One mutant identified lacks the response regulator gene roxR, which has not previously been reported to be involved regulating factors that facilitate interactions with lung epithelial cells. This finding suggests that RoxR likely regulates genes with relevance to P. aeruginosa mediated lung disease.

Salmonella pathogenesis and processing of secreted effectors by caspase-3.

The enteric pathogen Salmonella enterica serovar Typhimurium causes food poisoning resulting in gastroenteritis. The S. Typhimurium effector Salmonella invasion protein A (SipA) promotes gastroenteritis by functional motifs that trigger either mechanisms of inflammation or bacterial entry. During infection of intestinal epithelial cells, SipA was found to be responsible for the early activation of caspase-3, an enzyme that is required for SipA cleavage at a specific recognition motif that divided the protein into its two functional domains and activated SipA in a manner necessary for pathogenicity. Other caspase-3 cleavage sites identified in S. Typhimurium appeared to be restricted to secreted effector proteins, which indicates that this may be a general strategy used by this pathogen for processing of its secreted effectors.

The role of neutrophils in the event of intestinal inflammation.

The transmigration of polymorphonuclear leukocytes (PMNs; neutrophils) into the intestinal lumen is a classical phenomenon associated with a wide variety of disease states, including those of both pathogenic and autoimmune/idiopathic origin. While PMNs are highly effective at killing invading pathogens by releasing microbiocidal products, excessive or unnecessary release of these substances can cause substantial damage to the intestinal epithelium. Therefore, it is necessary to understand the underlying mechanisms that lure neutrophils into the lumen allowing them to perform their desired functions, so that researchers may begin to identify which processes may be potential targets for inhibiting the transmigration of PMNs during noninfectious states.

Saccharomyces boulardii interferes with Shigella pathogenesis by postinvasion signaling events.

Saccharomyces boulardii is gaining in popularity as a treatment for a variety of diarrheal diseases as well as inflammatory bowel disease. This study was designed to examine the effect of this yeast on infection by Shigella flexneri, a highly infectious and human host-adapted enteric pathogen. We investigated key interactions between the bacteria and host cells in the presence of the yeast in addition to a number of host responses including proinflammatory events and markers. Although the presence of the yeast during infection did not alter the number of bacteria that was able to attach or invade human colon cancer-derived T-84 cells, it did positively impact the tight junction protein zonula occluden-2 and significantly increase the barrier integrity of model epithelia. The yeast also decreased ERK, JNK, and NF-kappaB activation in response to S. flexneri, events likely responsible for the observed reductions in IL-8 secretion and the transepithelial migration of polymorphonuclear leukocytes across T-84 monolayers. These results, suggesting that the yeast allowed for a dampened inflammatory response, were confirmed in vivo utilizing a highly relevant model of human fetal colonic tissue transplanted into scid mice. Furthermore, a cell-free S. boulardii culture supernatant was also capable of reducing IL-8 secretion by infected T-84 cells. These data suggest that although the use of S. boulardii during infection with S. flexneri may alleviate symptoms associated with the inflammatory response of the host, it would not prevent infection.

Salmonella enterica serovar Typhimurium modulates P-glycoprotein in the intestinal epithelium.

Studies over the last decade have shown that Salmonella enterica serovar Typhimurium (S. typhimurium) is able to preferentially locate to sites of tumor growth and modulate (shrink) the growth of many cancers. Given this unique association between S. typhimurium and cancer cells, the objective of this study was to investigate the capacity of this microorganism to modulate the plasma membrane multidrug resistance (MDR) protein P-glycoprotein (P-gp), an ATP-binding cassette transporter responsible for effluxing many cancer drugs. Using an in vitro model of S. typhimurium infection of polarized human cancer intestinal cell lines, we have found that this enteric pathogen functionally downregulates the efflux capabilities of P-gp. Specifically, we show that S. typhimurium infection of human intestinal cancer cells results in the enhanced intracellular accumulation of a number of P-gp substrates that corresponds to the posttranscriptional downregulation of P-gp expression. Furthermore, cells expressing small interfering RNAs against MDR1, the gene encoding P-gp, were significantly more susceptible to the cytotoxic effects of bacterial infection. This result is consistent with our observation that S. typhimurium was significantly less able to invade cells overexpressing MDR1. Taken together, these results reveal a novel role for P-gp in the maintenance of homeostasis in the gastrointestinal tract in regard to bacterial infection. Thus the regulation of P-gp by S. typhimurium has important implications not only for the development of new cancer therapeutics aimed at reversing drug resistance but also in the understanding of how microbes have evolved diverse strategies to interact with their host.

nadA and nadB of Shigella flexneri 5a are antivirulence loci responsible for the synthesis of quinolinate, a small molecule inhibitor of Shigella pathogenicity.

The evolution of bacterial pathogens from commensal organisms involves virulence gene acquisition followed by pathoadaptation to the new host, including inactivation of antivirulence loci (AVL). AVL are core ancestral genes whose expression is incompatible with the pathogenic lifestyle. Previous studies identified cadA (encoding lysine decarboxylase) as an AVL of Shigella spp. In this study, AVL of Shigella were identified by examining a phenotypic difference from its non-pathogenic ancestor, Escherichia coli. Unlike most E. coli strains, Shigella spp. are nicotinic acid auxotrophs, the pathway for the de novo synthesis of NAD being uniformly defective. In Shigella flexneri, this defect is due to alterations in the nadA and/or nadB genes encoding the enzyme complex that converts L-aspartate to quinolinate, a precursor to NAD synthesis. Quinolinate was found to inhibit invasion and cell-to-cell spread of Sh. flexneri 5a and its ability to induce polymorphonuclear neutrophil transepithelial migration. Virulence of other Shigella species was also inhibited by quinolinate. Introduction of functional nadA and nadB genes from E. coli K-12 into Sh. flexneri 5a restored its ability to synthesize quinolinate but also resulted in strong attenuation of virulence in this strain. The results define nadA and nadB as AVL in Shigella and validate the concept of pathoadaptive evolution of bacteria from commensal ancestors by inactivation of AVL. They also suggest that studies focusing on this form of bacterial evolution can identify novel inhibitors of virulence in other bacterial pathogens.