A model of the isolated perfused rat small intestine

Effects of different ischemic preconditioning strategies on physiological and cellular mechanisms of intestinal ischemia/reperfusion injury: Implication from an isolated perfused rat small intestine model

Background

Intestinal ischemia/reperfusion (I/R)-injury often results in sepsis and organ failure and is of major importance in the clinic. A potential strategy to reduce I/R-injury is the application of ischemic preconditioning (IPC) during which repeated, brief episodes of I/R are applied. The aim of this study was to evaluate physiological and cellular effects of intestinal I/R-injury and to compare the influence of in-vivo IPC (iIPC) with ex-vivo IPC (eIPC), in which blood derived factors and nerval regulations are excluded.

Methods

Using an established perfused rat intestine model, effects of iIPC and eIPC on physiological as well as cellular mechanisms of I/R-injury (60 min hypoxia, 30 min reperfusion) were investigated. iIPC was applied by three reversible occlusions of the mesenteric artery in-vivo for 5 min followed by 5 min of reperfusion before isolating the small intestine, eIPC was induced by stopping the vascular perfusion ex-vivo 3 times for 5 min followed by 5 min of reperfusion after isolation of the intestine. Study groups (each N = 8–9 animals) were: iIPC, eIPC, I/R (iIPC group), I/R (eIPC group), iIPC+I/R, eIPC+I/R, no intervention/control (iIPC group), no intervention/control (eIPC group). Tissue morphology/damage, metabolic functions, fluid shifts and barrier permeability were evaluated. Cellular mechanisms were investigated using signaling arrays.

Results

I/R-injury decreased intestinal galactose uptake (iIPC group: p<0.001), increased vascular perfusion pressure (iIPC group: p<0.001; eIPC group: p<0.01) and attenuated venous flow (iIPC group: p<0.05) while lactate-to-pyruvate ratio (iIPC group, eIPC group: p<0.001), luminal flow (iIPC group: p<0.001; eIPC group: p<0.05), goblet cell ratio (iIPC group, eIPC group: p<0.001) and apoptosis (iIPC group, eIPC group: p<0.05) were all increased. Application of iIPC prior to I/R increased vascular galactose uptake (P<0.05) while eIPC had no significant impact on parameters of I/R-injury. On cellular level, I/R-injury resulted in a reduction of the phosphorylation of several MAPK signaling molecules. Application of iIPC prior to I/R increased phosphorylation of JNK2 and p38δ while eIPC enhanced CREB and GSK-3α/β phosphorylation.

Conclusion

Intestinal I/R-injury is associated with major physiological and cellular changes. However, the overall influence of the two different IPC strategies on the acute phase of intestinal I/R-injury is rather limited.

A novel histidine-tryptophan-ketoglutarate formulation ameliorates intestinal injury in a cold storage and ex vivo warm oxygenated reperfusion model in rats

AIM

The present study aims to evaluate protective effects of a novel histidine-tryptophan-ketoglutarate solution (HTK-N) and to investigate positive impacts of an additional luminal preservation route in cold storage-induced injury on rat small bowels.

METHODS

Male Lewis rats were utilized as donors of small bowel grafts. Vascular or vascular plus luminal preservation were conducted with HTK or HTK-N and grafts were stored at 4°C for 8 h followed by ex vivo warm oxygenated reperfusion with Krebs-Henseleit buffer for 30 min. Afterwards, intestinal tissue and portal vein effluent samples were collected for evaluation of morphological alterations, mucosal permeability and graft vitality.

RESULTS

The novel HTK-N decreased ultrastructural alterations but otherwise presented limited effect on protecting small bowel from ischemia-reperfusion injury in vascular route. However, the additional luminal preservation led to positive impacts on the integrity of intestinal mucosa and vitality of goblet cells. In addition, vascular plus luminal preservation route with HTK significantly protected the intestinal tissue from edema.

CONCLUSION

HTK-N protected the intestinal mucosal structure and graft vitality as a luminal preservation solution. Additional luminal preservation route in cold storage was shown to be promising.

Determination of intestinal permeability using in situ perfusion model in rats: Challenges and advantages to BCS classification applied to digoxin

The purpose of this work was to describe the closed loop in situ perfusion method in rats and to compare the difficulties and advantages with other methods proposed by regulatory agencies for BCS classification and finally to illustrate its application to evaluate the permeability of digoxin at relevant clinical concentrations. Digoxin was evaluated at two concentration levels: 1.0 μg/ml (with and without sodium azide 65.0 μg/ml) and 6.0 μg/ml. These concentrations correspond to the ratio of the highest dose strength (0.25 mg) and the highest single dose administered (1.5 mg) and the 250 ml of water. In situ closed loop perfusion studies in rats were performed in the whole small intestine and also in duodenum, jejunum and ileum segments to evaluate the relevance of P-gp secretion in the overall permeability. A kinetic modelling approach involving passive permeation and efflux transport mechanism allowed the estimation of the passive diffusional component and the Michaelis-menten parameters. The estimated K_m value demonstrated that at clinical luminal concentrations the efflux process is not saturated and then it could be inhibited by other drugs, excipients or food components leading to the already reported clinical drug-drug and drug-food interations. The present data confirms from a mechanistic point of view these interactions.

Signalling mechanisms in PAF-induced intestinal failure

Capillary leakage syndrome, vasomotor disturbances and gut atony are common clinical problems in intensive care medicine. Various inflammatory mediators and signalling pathways are involved in these pathophysiological alterations among them platelet-activating factor (PAF). The related signalling mechanisms of the PAF-induced dysfunctions are only poorly understood. Here we used the model of the isolated perfused rat small intestine to analyse the role of calcium (using calcium deprivation, IP-receptor blockade (2-APB)), cAMP (PDE-inhibition plus AC activator), myosin light chain kinase (inhibitor ML-7) and Rho-kinase (inhibitor Y27632) in the following PAF-induced malfunctions: vasoconstriction, capillary and mucosal leakage, oedema formation, malabsorption and atony. Among these, the PAF-induced vasoconstriction and hyperpermeability appear to be governed by similar mechanisms that involve IP3 receptors, extracellular calcium and the Rho-kinase. Our findings further suggest that cAMP-elevating treatments - while effective against hypertension and oedema - bear the risk of dysmotility and reduced nutrient uptake. Agents such as 2-APB or Y27632, on the other hand, showed no negative side effects and improved most of the PAF-induced malfunctions suggesting that their therapeutic usefulness should be explored.

Bioengineering of functional human induced pluripotent stem cell-derived intestinal grafts

Patients with short bowel syndrome lack sufficient functional intestine to sustain themselves with enteral intake alone. Transplantable vascularized bioengineered intestine could restore nutrient absorption. Here we report the engineering of humanized intestinal grafts by repopulating decellularized rat intestinal matrix with human induced pluripotent stem cell-derived intestinal epithelium and human endothelium. After 28 days of in vitro culture, hiPSC-derived progenitor cells differentiate into a monolayer of polarized intestinal epithelium. Human endothelial cells seeded via native vasculature restore perfusability. Ex vivo isolated perfusion testing confirms transfer of glucose and medium-chain fatty acids from lumen to venous effluent. Four weeks after transplantation to RNU rats, grafts show survival and maturation of regenerated epithelium. Systemic venous sampling and positron emission tomography confirm uptake of glucose and fatty acids in vivo. Bioengineering intestine on vascularized native scaffolds could bridge the gap between cell/tissue-scale regeneration and whole organ-scale technology needed to treat intestinal failure patients.

There is a need for humanised grafts to treat patients with intestinal failure. Here, the authors generate intestinal grafts by recellularizing native intestinal matrix with human induced pluripotent stem cell-derived epithelium and human endothelium, and show nutrient absorption after transplantation in rats.

Anti-inflammatory Effects of Fungal Metabolites in Mouse Intestine as Revealed by In vitro Models

Inflammatory bowel diseases (IBD), which include Crohn's disease and ulcerative colitis, are chronic inflammatory disorders that can affect the whole gastrointestinal tract or the colonic mucosal layer. Current therapies aiming to suppress the exaggerated immune response in IBD largely rely on compounds with non-satisfying effects or side-effects. Therefore, new therapeutical options are needed. In the present study, we investigated the anti-inflammatory effects of the fungal metabolites, galiellalactone, and dehydrocurvularin in both an in vitro intestinal inflammation model, as well as in isolated myenteric plexus and enterocyte cells. Administration of a pro-inflammatory cytokine mix through the mesenteric artery of intestinal segments caused an up-regulation of inflammatory marker genes. Treatment of the murine intestinal segments with galiellalactone or dehydrocurvularin by application through the mesenteric artery significantly prevented the expression of pro-inflammatory marker genes on the mRNA and the protein level. Comparable to the results in the perfused intestine model, treatment of primary enteric nervous system (ENS) cells from the murine intestine with the fungal compounds reduced expression of cytokines such as IL-6, TNF-α, IL-1β, and inflammatory enzymes such as COX-2 and iNOS on mRNA and protein levels. Similar anti-inflammatory effects of the fungal metabolites were observed in the human colorectal adenocarcinoma cell line DLD-1 after stimulation with IFN-γ (10 ng/ml), TNF-α (10 ng/ml), and IL-1β (5 ng/ml). Our results show that the mesenterially perfused intestine model provides a reliable tool for the screening of new therapeutics with limited amounts of test compounds. Furthermore, we could characterize the anti-inflammatory effects of two novel active compounds, galiellalactone, and dehydrocurvularin which are interesting candidates for studies with chronic animal models of IBD.

Lipid-associated oral delivery: Mechanisms and analysis of oral absorption enhancement

The majority of newly discovered oral drugs are poorly water soluble, and co-administration with lipids has proven effective in significantly enhancing bioavailability of some compounds with low aqueous solubility. Yet, lipid-based delivery technologies have not been widely employed in commercial oral products. Lipids can impact drug transport and fate in the gastrointestinal (GI) tract through multiple mechanisms including enhancement of solubility and dissolution kinetics, enhancement of permeation through the intestinal mucosa, and triggering drug precipitation upon lipid emulsion depletion (e.g., by digestion). The effect of lipids on drug absorption is currently not quantitatively predictable, in part due to the multiple complex dynamic processes that can be impacted by lipids. Quantitative mechanistic analysis of the processes significant to lipid system function and overall impact on drug absorption can aid in the understanding of drug-lipid interactions in the GI tract and exploitation of such interactions to achieve optimal lipid-based drug delivery. In this review, we discuss the impact of co-delivered lipids and lipid digestion on drug dissolution, partitioning, and absorption in the context of the experimental tools and associated kinetic expressions used to study and model these processes. The potential benefit of a systems-based consideration of the concurrent multiple dynamic processes occurring upon co-dosing lipids and drugs to predict the impact of lipids on drug absorption and enable rational design of lipid-based delivery systems is presented.

Adverse effects of hydroxyethyl starch (HES 130/0.4) on intestinal barrier integrity and metabolic function are abrogated by supplementation with Albumin

Background

Volume resuscitation with hydroxyethyl starch (HES) is controversially discussed and we recently showed that HES perfusion impairs endothelial and epithelial intestinal barrier integrity. Here we investigated whether Albumin containing HES solutions are superior to HES alone in maintaining intestinal barrier function.

Methods

An isolated perfused model of the mouse small intestine was used to investigate the effects of: (i) 3 % Albumin (Alb), (ii) 3 % HES or (iii) 1.5 % HES/1.5 % Albumin (HES/Alb). Intestinal morphology, cell damage, metabolic functions, fluid shifts and endothelial/epithelial barrier permeability were evaluated. Potentially involved signaling mechanisms (Erk1/2, Akt and Stat5 phosphorylation) were screened.

Results

HES induced histomorphological damage (p < 0.01 vs. Alb), by trend elevated the amount of luminal intestinal fatty acid binding protein and reduced galactose uptake (p < 0.001 vs. Alb). Luminal and lymphatic flow rates were increased (p < 0.001 vs. Alb), while vascular flow was decreased (p < 0.001 vs. Alb) during HES perfusion. HES also increased the vascular to luminal FITC-dextran transfer (p < 0.001 vs. Alb), pointing towards a fluid shift from the vascular to the luminal and lymphatic compartments during HES perfusion. Addition of Alb (HES/Alb) reversed all adverse effects of HES (p < 0.05 vs. HES), restored barrier integrity (p < 0.05 vs. HES) and improved metabolic function of the intestine (p < 0.001 vs. HES; p < 0.05 vs. Alb). Mechanistically, HES/Alb perfusion resulted in an increased phosphorylation of Erk1/2 and Akt kinases (p < 0.001 vs. HES), while Stat5 remained unchanged.

Conclusions

Albumin supplementation abrogates the adverse effects of HES in the intestine and underlying mechanism may function via phosphorylation of Erk1/2 and Akt. Albumin containing HES solutions are superior to HES alone and may improve the suitability of HES in the clinic.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0810-3) contains supplementary material, which is available to authorized users.

Ex vivo perfusion of the isolated rat small intestine as a novel model of Salmonella enteritis

Using an ex vivo perfused rat small intestinal model, we examined pathological changes to the tissue, inflammation induction, as well as dynamic changes to smooth muscle activity, metabolic competence, and luminal fluid accumulation during short-term infection with the enteropathogenic bacteria Salmonella enterica serovar Typhimurium and Yersinia enterocolitica. Although few effects were seen upon Yersinia infection, this system accurately modeled key aspects associated with Salmonella enteritis. Our results confirmed the importance of the Salmonella Pathogenicity Island 1 (SPI1)-encoded type 3 secretion system (T3SS) in pathology, tissue invasion, inflammation induction, and fluid secretion. Novel physiological consequences of Salmonella infection of the small intestine were also identified, namely, SPI-1-dependent vasoconstriction and SPI-1-independent reduction in the digestive and absorptive functions of the epithelium. Importantly, this is the first small animal model that allows for the study of Salmonella-induced fluid secretion. Another major advantage of this model is that one can specifically determine the contribution of resident cell populations. Accordingly, we can conclude that recruited cell populations were not involved in the pathological damage, inflammation induction, fluid accumulation, nutrient absorption deficiency, and vasoconstriction observed. Although fluid loss induced by Salmonella infection is hypothesized to be due to damage caused by recruited neutrophils, our data suggest that bacterial invasion and inflammation induction in resident cell populations are sufficient for fluid loss into the lumen. In summary, this model is a novel and useful tool that allows for detailed examination of the early physiopathological effects of Salmonella infection on the small intestine.

Long-term remote organ consequences following acute kidney injury

Acute kidney injury (AKI) has been a global health epidemic problem with soaring incidence, increased long-term risks for multiple comorbidities and mortality, as well as elevated medical costs. Despite the improvement of patient outcomes following the advancements in preventive and therapeutic strategies, the mortality rates among critically ill patients with AKI remain as high as 40–60 %. The distant organ injury, a direct consequence of deleterious systemic effects, following AKI is an important explanation for this phenomenon. To date, most evidence of remote organ injury in AKI is obtained from animal models. Whereas the observations in humans are from a limited number of participants in a relatively short follow-up period, or just focusing on the cytokine levels rather than clinical solid outcomes. The remote organ injury is caused with four underlying mechanisms: (1) “classical” pattern of acute uremic state; (2) inflammatory nature of the injured kidneys; (3) modulating effect of AKI of the underlying disease process; and (4) healthcare dilemma. While cytokines/chemokines, leukocyte extravasation, oxidative stress, and certain channel dysregulation are the pathways involving in the remote organ damage. In the current review, we summarized the data from experimental studies to clinical outcome studies in the field of organ crosstalk following AKI. Further, the long-term consequences of distant organ-system, including liver, heart, brain, lung, gut, bone, immune system, and malignancy following AKI with temporary dialysis were reviewed and discussed.

Gastrointestinal Safety Pharmacology in Drug Discovery and Development

Although the basic structure of the gastrointestinal tract (GIT) is similar across species, there are significant differences in the anatomy, physiology, and biochemistry between humans and laboratory animals, which should be taken into account when conducting a gastrointestinal (GI) assessment. Historically, the percentage of cases of drug attrition associated with GI-related adverse effects is small; however, this incidence has increased over the last few years. Drug-related GI effects are very diverse, usually functional in nature, and not limited to a single pharmacological class. The most common GI signs are nausea and vomiting, diarrhea, constipation, and gastric ulceration. Despite being generally not life-threatening, they can greatly affect patient compliance and quality of life. There is therefore a real need for improved and/or more extensive GI screening of candidate drugs in preclinical development, which may help to better predict clinical effects. Models to identify drug effects on GI function cover GI motility, nausea and emesis liability, secretory function (mainly gastric secretion), and absorption aspects. Both in vitro and in vivo assessments are described in this chapter. Drug-induced effects on GI function can be assessed in stand-alone safety pharmacology studies or as endpoints integrated into toxicology studies. In silico approaches are also being developed, such as the gut-on-a-chip model, but await further optimization and validation before routine use in drug development. GI injuries are still in their infancy with regard to biomarkers, probably due to their greater diversity. Nevertheless, several potential blood, stool, and breath biomarkers have been investigated. However, additional validation studies are necessary to assess the relevance of these biomarkers and their predictive value for GI injuries.

Hydroxyethyl starch (HES 130/0.4) impairs intestinal barrier integrity and metabolic function: findings from a mouse model of the isolated perfused small intestine

BACKGROUND

The application of hydroxyethyl starch (HES) for volume resuscitation is controversially discussed and clinical studies have suggested adverse effects of HES substitution, leading to increased patient mortality. Although, the intestine is of high clinical relevance and plays a crucial role in sepsis and inflammation, information about the effects of HES on intestinal function and barrier integrity is very scarce. We therefore evaluated the effects of clinically relevant concentrations of HES on intestinal function and barrier integrity employing an isolated perfused model of the mouse small intestine.

METHODS

An isolated perfused model of the mouse small intestine was established and intestines were vascularly perfused with a modified Krebs-Henseleit buffer containing 3% Albumin (N=7) or 3% HES (130/0.4; N=7). Intestinal metabolic function (galactose uptake, lactate-to-pyruvate ratio), edema formation (wet-to-dry weight ratio), morphology (histological and electron microscopical analysis), fluid shifts within the vascular, lymphatic and luminal compartments, as well as endothelial and epithelial barrier permeability (FITC-dextran translocation) were evaluated in both groups.

RESULTS

Compared to the Albumin group, HES perfusion did not significantly change the wet-to-dry weight ratio and lactate-to-pyruvate ratio. However, perfusing the small intestine with 3% HES resulted in a significant loss of vascular fluid (p<0.01), an increased fluid accumulation in the intestinal lumen (p<0.001), an enhanced translocation of FITC-dextran from the vascular to the luminal compartment (p<0.001) and a significantly impaired intestinal galactose uptake (p<0.001). Morphologically, these findings were associated with an aggregation of intracellular vacuoles within the intestinal epithelial cells and enlarged intercellular spaces.

CONCLUSION

A vascular perfusion with 3% HES impairs the endothelial and epithelial barrier integrity as well as metabolic function of the small intestine.

Quinidine, but not eicosanoid antagonists or dexamethasone, protect the gut from platelet activating factor-induced vasoconstriction, edema and paralysis

Intestinal circulatory disturbances, atony, edema and swelling are of great clinical relevance, but the related mechanisms and possible therapeutic options are poorly characterized, in part because of the difficulties to comprehensively analyze these conditions. To overcome these limitations we have developed a model of the isolated perfused rat small intestine where all of these symptoms can be studied simultaneously. Here we used this model to study the role of eicosanoids, steroids and quinidine in platelet-activating factor (PAF)-induced intestinal disorders. A vascular bolus of PAF (0.5 nmol) triggered release of thromboxane and peptidoleukotrienes into the vascular bed (peak concentration 35 nM and 0.8 nM) and reproduced all symptoms of intestinal failure: mesenteric vasoconstriction, translocation of fluid and macromolecules from the vasculature to the lumen and lymphatics, intestinal edema formation, loss of intestinal peristalsis and decreased galactose uptake. All effects of PAF were abolished by the PAF-receptor antagonist ABT491 (2.5 μM). The COX and LOX inhibitors ASA and AA861 (500 μM, 10 μM) did not exhibit barrier-protective effects and the eicosanoid antagonists SQ29548 and MK571 (10 μM, each) only moderately attenuated the loss of vascular fluid, the redistribution to the lumen and the transfer of FITC dextran to the lumen. The steroid dexamethasone (10 μM) showed no barrier-protective properties and failed to prevent edema formation. Quinidine (100 μM) inhibited the increase in arterial pressure, stabilized all the intestinal barriers, and reduced lymph production and the transfer of FITC dextran to the lymph. While quinidine by itself reduced peristalsis, it also obviated paralysis, preserved intestinal functions and prevented edema formation. We conclude that quinidine exerts multiple protective effects against vasoconstriction, edema formation and paralysis in the intestine. The therapeutic use of quinidine for intestinal ailments deserves further study.

Motility patterns of ex vivo intestine segments depend on perfusion mode

AIM: To evaluate and characterize motility patterns from small intestinal gut segments depending on different perfusion media and pressures.

METHODS: Experiments were carried out in a custom designed perfusion chamber system to validate and standardise the perfusion technique used. The perfusion chamber was built with a transparent front wall allowing for optical motility recordings and a custom made fastener to hold the intestinal segments. Experiments with different perfusion and storage media combined with different luminal pressures were carried out to evaluate the effects on rat small intestine motility. Software tools which enable the visualization and characterization of intestinal motility in response to different stimuli were used to evaluate the videotaped experiments. The data collected was presented in so called heatmaps thus providing a concise overview of form and strength of contractility patterns. Furthermore, the effect of different storage media on tissue quality was evaluated. Haematoxylin-Eosin stainings were used to compare tissue quality depending on storage and perfusion mode.

RESULTS: Intestinal motility is characterized by different repetitive motility patterns, depending on the actual situation of the gut. Different motility patterns could be recorded and characterized depending on the perfusion pressure and media used. We were able to describe at least three different repetitive patterns of intestinal motility in vitro. Patterns with an oral, anal and oro-anal propagation direction could be recorded. Each type of pattern finalized its movement with or without a subsequent distension of the wavefront. Motility patterns could clearly be distinguished in heatmap diagrams. Furthermore undirected motility could be observed. The quantity of the different patterns varies and is highly dependent on the perfusion medium used. Tissue preservation varies depending on the perfusion medium utilized, therefore media with a simple composition as Tyrode solution can only be recommended for short time experiments. The more complex media, MEM-HEPES medium and especially AQIX^® RS-I tissue preservation reagent preserved the tissue much better during perfusion.

CONCLUSION: Perfusion media have to be carefully chosen considering type and duration of the experiments. If excellent tissue quality is required, complex media are favorable. Perfusion pressure is also of great importance due to the fact that a minimum amount of luminal pressure seems to be necessary to trigger intestinal contractions.

The gut wall provides an effective barrier against nanoparticle uptake

BACKGROUND

The omnipresence of nanoparticles (NPs) in numerous goods has led to a constant risk of exposure and inadvertent uptake for humans. This situation calls for thorough investigation of the consequences of NP intake. As the vast mucosa of the human gastrointestinal tract represents an attractive site of entry, we wanted to take a look on the fate that ingested NPs suffer in the gut. As a model to investigate NP uptake we used the isolated perfused rat small intestine. Differently sized fluorescent latex particles were used as exemplary anthropogenic NPs.

RESULTS

The particles were administered as bolus into the isolated intestine, and samples from the luminal, vascular and lymphatic compartments were collected over time. NP amounts in the different fluids were determined by fluorescence measurements. No particles could be detected in the vascular and lymphatic system. By contrast a major amount of NPs was found in luminal samples. Yet, a substantial share of particles could not be recovered in the fluid fractions, indicating a sink function of the intestinal tissue for NPs. A histological examination of the gut revealed that virtually no particles adhered to the epithelium or resided in the tissue, the bulk of particles seemed to be trapped in the mucus lining the gut tube. When this mucus was dissolved and removed from the gut almost the entire amount of particles missing could be recovered: over 95% of the given NPs were present in the two fractions, the luminal samples and the dissolved mucus. To foster NP uptake via an extended interaction time with the epithelium, the intestinal peristalsis was decelerated and the duration of the experiment was prolonged. Even under those conditions, no particle fluorescence was detected in the vascular and lymphatic samples.

CONCLUSION

We could show that after intestinal exposure with a large dose of NPs the vast majority of NPs did obviously not come into contact with the epithelium but was either directly discarded from the gut or trapped in mucus. The healthy small intestinal tract evidently provides an effective barrier against NP uptake whereby the mucus film seems to play an important role.

Iron metabolism in aerobes: managing ferric iron hydrolysis and ferrous iron autoxidation

Aerobes and anaerobes alike express a plethora of essential iron enzymes; in the resting state, the iron atom(s) in these proteins are in the ferrous state. For aerobes, ferric iron is the predominant environmental valence form which, given ferric iron's aqueous chemistry, occurs as 'rust', insoluble, bio-inert polymeric ferric oxide that results from the hydrolysis of [Fe(H(2)O)(6)](3+). Mobilizing this iron requires bio-ferrireduction which in turn requires managing the rapid autoxidation of the resulting Fe(II) which occurs at pH > 6. This review examines the aqueous redox chemistry of iron and the mechanisms evolved in aerobes to suppress the 'rusting out' of Fe(III) and the ROS-generating autoxidation of Fe(II) so as to make this metal ion available as the most ubiquitous prosthetic group in metallobiology.

Ingestion of (n-3) fatty acids augments basal and platelet activating factor-induced permeability to dextran in the rat mesenteric vascular bed

Loss of intestinal barrier function and subsequent edema formation remains a serious clinical problem leading to hypoperfusion, anastomotic leakage, bacterial translocation, and inflammatory mediator liberation. The inflammatory mediator platelet activating factor (PAF) promotes eicosanoid-mediated edema formation and vasoconstriction. Fish oil-derived (n-3) fatty acids (FA) favor the production of less injurious eicosanoids but may also increase intestinal paracellular permeability. We hypothesized that dietary (n-3) FA would ameliorate PAF-induced vasoconstriction and enhance vascular leakage of dextran tracers. Rats were fed either an (n-3) FA-rich diet (EPA-rich diet; 4.0 g/kg EPA, 2.8 g/kg DHA) or a control diet (CON diet; 0.0 g/kg EPA and DHA) for 3 wk. Subsequently, isolated and perfused small intestines were stimulated with PAF and arterial pressure and the translocation of fluid and macromolecules from the vasculature to lumen and lymphatics were analyzed. In intestines of rats fed the EPA-rich diet, intestinal phospholipids contained up to 470% more EPA and DHA at the expense of arachidonic acid (AA). The PAF-induced increase in arterial pressure was not affected by the EPA-rich diet. However, PAF-induced fluid loss from the vascular perfusate was higher in intestines of rats fed the EPA-rich diet. This was accompanied by a greater basal loss of dextran from the vascular perfusate and a higher PAF-induced transfer of dextran from the vasculature to the lumen (P = 0.058) and lymphatics. Our data suggest that augmented intestinal barrier permeability to fluid and macromolecules is a possible side effect of (n-3) FA-rich diet supplementation.

Engineering the Lymphatic System

The recent advances in our understanding of lymphatic physiology and the role of the lymphatics in actively regulating fluid balance, lipid transport, and immune cell trafficking has been furthered in part through innovations in imaging, tissue engineering, quantitative biology, biomechanics, and computational modeling. Interdisciplinary and bioengineering approaches will continue to be crucial to the progression of the field, given that lymphatic biology and function are intimately woven with the local microenvironment and mechanical loads experienced by the vessel. This is particularly the case in lymphatic diseases such as lymphedema where the microenvironment can be drastically altered by tissue fibrosis and adipocyte accumulation. In this review we will highlight contributions engineering and mechanics have made to lymphatic physiology and will discuss areas that will be important for future research.

Mechanisms of chylomicron uptake into lacteals

Right from birth, the lymphatics play a crucial role in dietary functions. A majority of the lipid absorbed from the newborn's lipid-rich diet enters the blood circulation through the lymphatic system, which transports triglyceride-loaded particles known as chylomicrons from the villi of the small intestine to the venous circulation near the heart. In light of the significance of this role, as well as the fact that lipid transport from the gut was one of the earliest discovered functions of the lymphatic vasculature, it is surprising that so little is known about how chylomicrons initially gain access to the lymphatic vessel. This review will focus on the current mechanisms thought to be important in this process and highlight important questions that need to be answered in the future.

Quantitation of major protein constituents of murine intestinal fluid

The gastrointestinal tract is a hostile biological environment, yet not all ingested materials are destroyed. The minute differences that determine whether a substance persists or is digested, liberated, adsorbed, excreted, or taken up are still poorly understood. Most attempts to investigate the events occurring during an orogastrointestinal passage rely on simplified in vitro systems where an analyte is exposed to artificial intestinal fluids. To closely mimic the events in the gastrointestinal tract, the exact intestinal fluid composition and the in vivo concentration of its constituents must be known. The widely used lavage procedures, however, dilute the intestinal fluids to an extent that precludes recalculation to the original concentrations. Thus, we developed procedures with which undiluted murine intestinal fluid can be harvested; determined the in vivo concentrations of the digestive enzymes trypsin, chymotrypsin, and elastase and the adsorbents mucin and immunoglobulin A in small intestinal fluid of fasted and unfasted female Balb/c mice; and identified chymotrypsin and immunoglobulin A as valid endogenous dilution markers for the recalculation of aqueous lavages. With these technologies and information at hand, more reliable investigations on the fate of allergens, pathogens, food, and anthropogenic xenobiotics in the gastrointestinal tract will be possible.

Lymphatic lipid transport: sewer or subway?

The lymphatics began receiving attention in the scientific community as early as 1622, when Gasparo Aselli noted the appearance of milky-white vessels in the mesentery of a well-fed dog. Since this time, the lymphatic system has been historically regarded as the sewer of the vasculature, passively draining fluid and proteins from the interstitial spaces (along with lipid from the gut) into the blood. Recent reports, however, suggest that the lymphatic role in lipid transport is an active and intricate process, and that when lymphatic function is compromised, there are systemic consequences to lipid metabolism and transport. This review highlights these recent findings, and suggests future directions for understanding the interplay between lymphatic and lipid biology in health and disease.