Lumen Of Gastrointestinal Tract Research Articles

Microbial Translocation and Infectious Diseases: What Is the Link?

Microbial Translocation and Infectious Diseases: What Is the Link?

Identification of Bacteria in Paraffin-Embedded Tissues Using 16S rDNA Sequencing from a Neonate with Necrotizing Enterocolitis

The conventional approach to bacterial identification in paraffin-embedded tissue relies mainly on morphology, with the aid of Gram stain. This approach is only able to provide some clues; it does not offer the capability of accurate identification. Bacterial identification based on sequencing of 16S ribosomal DNA (rDNA) is able to identify bacteria to the species level. Here we demonstrate the application of this technique in the postmortem examination, for which we had obtained different results from premortem and postmortem blood cultures. In the postmortem examination, abundant gram-negative rods were present in gastrointestinal tract lumen and lymphatic space. DNA was extracted from paraffin-embedded tissue of the above sections and subjected to 16S rDNA polymerase chain reaction for the first 500 base pairs, followed by sequencing. The results of sequencing correlated well with the postmortem culture result. In this review, the newly emerging field of bacterial identification with molecular techniques employing both broad-range and targeted approaches and their clinical applications and limitations are discussed.

UT-B1 Mediates Transepithelial Urea Flux in the Rat Gastrointestinal Tract

The process of urea nitrogen salvaging plays a vital role in the symbiotic relationship between mammals and their intestinal bacteria. The first step in this process requires the movement of urea from the mammalian bloodstream into the gastrointestinal tract lumen via specialized proteins known as facilitative urea transporters. In this study, we examined both transepithelial urea fluxes and urea transporter protein abundance along the length of the rat gastrointestinal tract. Urea flux experiments that used rat gastrointestinal tissues showed significantly higher transepithelial urea transport was present in caecum and proximal colon (P < 0.01, n = 8, analysis of variance [ANOVA]). This large urea flux was significantly inhibited by 1,3,dimethylurea (P < 0.001, n = 8, ANOVA) and thiourea (P < 0.05, n = 6, unpaired t-test), both known blockers of facilitative urea transporters. Immunoblotting analysis failed to detect any UT-A protein within rat gastrointestinal tissue protein samples. In contrast, a 30-kDa UT-B1 protein was strongly detected in both caecum and proximal colon samples at significantly higher levels compared to the rest of the gastrointestinal tract (P < 0.01, n = 4, ANOVA). We therefore concluded that UT-B1 mediates the transepithelial movement of urea that occurs in specific distal regions of the rat gastrointestinal tract.

Modulation of Shigella virulence in response to available oxygen in vivo

Bacteria coordinate expression of virulence determinants in response to localized microenvironments in their hosts. Here we show that Shigella flexneri, which causes dysentery, encounters varying oxygen concentrations in the gastrointestinal tract, which govern activity of its type three secretion system (T3SS). The T3SS is essential for cell invasion and virulence. In anaerobic environments (for example, the gastrointestinal tract lumen), Shigella is primed for invasion and expresses extended T3SS needles while reducing Ipa (invasion plasmid antigen) effector secretion. This is mediated by FNR (fumarate and nitrate reduction), a regulator of anaerobic metabolism that represses transcription of spa32 and spa33, virulence genes that regulate secretion through the T3SS. We demonstrate there is a zone of relative oxygenation adjacent to the gastrointestinal tract mucosa, caused by diffusion from the capillary network at the tips of villi. This would reverse the anaerobic block of Ipa secretion, allowing T3SS activation at its precise site of action, enhancing invasion and virulence.

Physiologically Based Pharmacokinetic Modeling of Deltamethrin: Development of a Rat and Human Diffusion-Limited Model

Mirfazaelian et al. developed a physiologically based pharmacokinetic (PBPK) model for the pyrethroid pesticide deltamethrin in the rat. This model describes gastrointestinal (GI) tract absorption as a saturable process mediated by phase III efflux transporters which pump deltamethrin out of the intestinal enterocytes into the GI tract lumen, resulting in minimal net absorption at low concentrations and increasing absorption at higher concentrations. In the present study, the dose dependency in absorption of deltamethrin was examined in male Long Evans rats using po exposures predicted by the Mirfazaelian model to yield different po bioavailability values. No difference in the bioavailability from single po doses of 0.3 and 3.0 mg/kg deltamethrin was observed. Based on this finding, the Mirfazaelian PBPK model was modified to exclude a saturable absorption process. Other changes to the Mirfazaelian model included describing all tissue compartments with diffusion-limited kinetics and a single blood compartment. These changes improved model predictions of deltamethrin tissue concentration data from the present study and the literature. The rat model was then scaled to humans. The model predicted a twofold greater peak deltamethrin brain concentration and threefold greater area under the curve (AUC(0-48 h)) for humans following an po exposure of 1 mg/kg. Based on this model, humans would have greater distribution of deltamethrin to the brain for the same administered po dose compared to rats. The relative sensitivity to deltamethrin between rats and humans depends on both pharmacokinetic and pharmacodynamic differences. Species differences in the pharmacodynamic responses to deltamethrin between rats and humans remain uncharacterized.

PATHOPHYSIOLOGY OF LPS-INDUCED GASTROINTESTINAL INJURY IN THE RAT

A hydrophobic layer of phosphatidylcholine (PC) overlies and protects the surface of the gastrointestinal (GI) tract, contributing to barrier integrity. During critical illness such as sepsis, gut barrier integrity is compromised, which could be related to degradation of PC. The purpose of this study was to investigate a role for luminal (secretory) phospholipase A2 (sPLA(2)) in LPS-induced GI injury. Rats were treated with LPS (5 mg/kg) or saline for 0.5, 1, 3, and 5 h. The gastric and ileal luminal contents were collected for determination of sPLA(2) activity, and the luminal lipids were analyzed using thin layer chromatography for lyso-PC content. The GI permeability was assessed in vivo with fluorescein-isothiocyanate dextran 4000 and rats were tested with or without a specific sPLA(2) inhibitor. LPS induced significant increases in sPLA(2) activity and lyso-PC content in the gastric and ileal lumens at 5 h. In addition, LPS treated rats showed a significant increase in GI permeability to fluorescein-isothiocyanate dextran in both the stomach and ileum at 5 h, which was prevented by pretreatment with the sPLA(2) inhibitor. In response to LPS, sPLA(2) activity increases in the GI tract lumen where it may degrade the extracellular protective phospholipid layer and membranes, producing injurious lyso-PC and increased GI permeability. Pretreatment with an orally active sPLA(2) inhibitor blocks the LPS-induced increase in GI permeability, and may suggest a new approach to fortify the GI mucosal barrier and prevent complications from endotoxin in trauma and other patients.

Genetic Modification of Somatic Gut Mucosa

Genetic Modification of Somatic Gut Mucosa

Evaluation of the effects of the opioid agonist morphine on gastrointestinal tract function in horses

To evaluate the effects of morphine administration for 6 days on gastrointestinal tract function in healthy adult horses. 5 horses. Horses were randomly allocated into 2 groups in a crossover study. Horses in the treatment group received morphine sulfate at a dosage of 0.5 mg/kg, IV, every 12 hours for 6 days. Horses in the control group received saline (0.9% NaCl) solution at a dosage of 10 mL, IV, every 12 hours for 6 days. Variables assessed included defecation frequency, weight of feces produced, intestinal transit time (evaluated by use of barium-filled spheres and radiographic detection in feces), fecal moisture content, borborygmus score, and signs of CNS excitement and colic. Administration of morphine resulted in gastrointestinal tract dysfunction for 6 hours after each injection. During those 6 hours, mean +/- SD defecation frequency decreased from 3.1 +/- 1 bowel movements in control horses to 0.9 +/- 0.5 bowel movements in treated horses, weight of feces decreased from 4.1 +/- 0.7 kg to 1.1 +/- 0.7 kg, fecal moisture content decreased from 76 +/- 2.7% to 73.5 +/- 2.9%, and borborygmus score decreased from 13.2 +/- 2.9 to 6.3 +/- 3.9. Mean gastrointestinal transit time was also increased, compared with transit times in control horses. Morphine administered at 0.5 mg/kg twice daily decreased propulsive motility and moisture content in the gastrointestinal tract lumen. These effects may predispose treated horses to development of ileus and constipation.

A dissolução in vitro na previsão da absorção oral de fármacos em formas farmacêuticas de liberação modificada

Pretende-se com o presente trabalho abordar os aspectos teóricos e práticos dos estudos de dissolução das formas farmacêuticas sólidas orais de liberação modificada, em três partes. Na primeira parte faz-se referência à classificação, interesse terapêutico e teoria da liberação do fármaco. Na segunda parte abordam-se as teorias de dissolução, os modelos de liberação, os sistemas de dissolução e sua validação, as especificações e critérios de aceitação dos ensaios de dissolução e ainda os fatores condicionantes da dissolução, liberação e absorção. Na terceira parte confrontamse as condições em que são efetuados os ensaios de dissolução com os parâmetros fisiológicos, fazendo referência aos meios de dissolução e composição do lume do trato gastrintestinal e aos modelos hidrodinâmicos.

Pathogenesis, treatment, and therapeutic trials in hemolytic uremic syndrome.

Diarrhea-associated hemolytic uremic syndrome is one of the most common causes of acute renal failure in childhood. Nearly all cases are the result of an antecedent infection by Shiga toxin--producing strains of Escherichia coli, especially the O157:H7 serotype. Most cases occur after ingestion of contaminated meat; however, new food sources such as leaf lettuce, alfalfa sprouts, and goat's milk have been identified, and diarrhea-associated hemolytic uremic syndrome can occur after exposure to contaminated water in recreational swimming sites. Diarrhea-associated hemolytic uremic syndrome is a systemic disease with activation of a variety of inflammatory cytokines. Kidney injury may result from direct effects of the Shiga toxin on renal tubular epithelial cells as well as endothelial cells. Early diagnosis of diarrhea-associated hemolytic uremic syndrome may be expedited by the introduction of new techniques to rapidly detect toxin and microorganism in stool samples. Optimal therapy of diarrhea-associated hemolytic uremic syndrome includes intensive management of the renal failure and serious extrarenal complications that may occur during the course of disease. The role of antibiotics in prevention and amelioration of diarrhea-associated hemolytic uremic syndrome remains controversial. Experimental therapies that are undergoing evaluation in clinical trials include SYNSORB Pk (SYNSORB Biotech, Inc., Calgary, Alberta, Canada), a drug designed to bind Shiga toxin in the lumen of gastrointestinal tract. Immunization strategies are also being developed and tested. It is hoped that with continued progress in this field the incidence of diarrhea-associated hemolytic uremic syndrome in children will be substantially reduced in the coming years.

Enterohemorrhagic Escherichia coli O157: H7 Infection.

The first recognized outbreaks of hemorrhagic colitis occurred in 1982 in the United State and its etiologic agent was identified to be Escherichia coli O157 : H7, a serotype not previously associated with diseases in humans. In Japan, isolates of the serotype O157 : H7 from contaminated drinking water were first implicated in an outbreak occurred in 1990 in a kindergarten of the Saitama Prefecture, and at least other 12 such outbreaks have been recorded in 1993-1995. In the year 1996, unprecedentedly large outbreaks and many sporadic cases of disease caused by E. coli O157 : H7 occurred in various parts of Japan, affecting more than 9000 people in total (11 deaths). In most cases, however, the ultimate source of the infection could not be traced. Although many different serotypes of E. coli, which are collectively referred to as enterohemorrhagic E. coli (EHEC), were found to cause bloody diarrhea, the serotype O157 : H7 has been recognized worldwide as the pathogen associated most frequently with serious complications known as hemolytic colitis and hemolytic uremic syndrome. E. coli O157 : H7 is characteristic of a low infectious dose, on the order of a few hundred organisms, which contributes to the spread of the infection in outbreak situations. Cattle are considered to be the major reservoir of EHEC including O157 : H7. EHEC strains produce at least two immunologically distinct cytotoxins that closely resemble the Shiga toxin produced by the Shigella dysenteriae type 1 strains. These toxins (called Shiga-like toxins or Vero toxins) appear to be responsible for causing many pathological effects associated with EHEC infections. However, how the toxins move from the intestinal tract lumen to the sites where they damage the kidney remains to be evaluated. Moreover, there are some doubts about the value of antibiotic therapy in such infections because of the observation that some antibiotics can increase the toxin expression in vitro and because of the concern that EHEC which are lysing due to their actions in the gastrointestinal tract lumen may actually release more toxin than do intact bacterial cells. Unique biochemical characteristics of E. coli O157 : H7-it ferments sorbitol very slowly and usually does not make β-glucuronidase- are used to differentiate this strain from other enteric E. coli strains. Alternative methods based on the detection of the toxins themselves by enzyme immunoassay are employed in parallel. This review describes the current understanding of the infectious disease caused by E. coli O157 : H7, with an emphasis on the main diagnostic tests and epidemiology for this serotype and the role of the toxins in pathogenesis.

Transfer of functional immunoglobulin G (IgG) antibody into the gastrointestinal tract accounts for IgG clearance in calves

The transfer of circulating immunoglobulin G1 (IgG1) antibody to the gastrointestinal tract in young calves was quantified by using bovine anti-dinitrophenol IgG1 antibody labeled with 125I. The antibody was administered to newborn calves by intravenous injection, and transfer of the labeled IgG1 to the gastrointestinal tract occurred as demonstrated by excretion of protein-bound label in the feces and by the presence of the labeled IgG1 antibody in the gastrointestinal tract lumen at necropsy. Sixty-eight percent of the [125I]IgG1 clearance occurred by transfer to the gastrointestinal tract. Protein-bound 125I in the gastrointestinal tract lumen retained 65% of the specific dinitrophenol-binding ability of the labeled antibody originally administered. These results show that (i) transfer to the intestinal lumen is the major means of IgG1 clearance in calves, and (ii) this transfer results in antigen-binding antibody in the intestinal tract lumen. The potential contribution to enteric immunity of IgG1 reaching the intestinal lumen from circulation remains to be determined.

Effect of 90 Y Inhaled in Fused Clay Particles on the Gastrointestinal Tract of Beagles

Ten beagles were exposed by inhalation to aerosols of ${}^{90}{\rm Y}$ in fused clay particles to study the radiation dose to the gastrointestinal (GI) tract and effects resulting from clearance of the upper respiratory tract after the deposition of high initial body burdens of inhaled ${}^{90}{\rm Y}$. Focal colonic lesions were found in two dogs, 8 and 12 days after inhalation of ${}^{90}{\rm Y}$ that resulted in GI burdens (GIB) of 18 and 34 mCi. Similar, but less severe, lesions were found in two dogs sacrificed 27 days after exposure with GIBs of 18 and 32 mCi. No GI lesions were found in six dogs with GIBs of 9-18 mCi. Two of the 10 dogs had thermoluminescent dosimeters surgically implanted in the GI tract lumen and submucosa. The highest radiation doses were measured in the colon. One dog, with measured doses to the colon of 3200-5700 rads, had focal colitis when sacrificed 8 days after exposure. The other dog, with doses to colon of 1000-2800 rads had no GI lesions at sacrifice 8 days after exposu...