Dose Effects of Apical versus Basolateral Zinc Supplementation on Epithelial Resistance,Viability, and Metallothionein Expression in Two Intestinal Epithelial Cell Lines

Zinc supplementation is used to reduce diarrhea incidence in piglets and it has been shown in vitro that the antisecretory effects are maximal after basolateral zinc application. To examine whether the application site and dose of zinc also influence passive ion permeability and viability, porcine (IPEC‐J2) and human (Caco‐2) intestinal epithelial cells were treated with increasing zinc concentrations (0–200 μM) at either the apical or basolateral side. Transepithelial electrical resistance and viability decreased and expression of metallothionein and the efflux zinc transporter 1 increased most prominently when zinc was added in high concentrations at the basolateral side of IPEC‐J2 cells. Zinc transporter 4, a zinc importer, was not affected. Heat shock protein 70 mRNA expression increased only after basolateral addition of 200 μM zinc in IPEC‐J2 cells. Thus, zinc can elicit toxic effects especially when added at the basolateral side, with IPEC‐J2 cells being more susceptible than Caco‐2 cells.     

Increased intracellular calcium level and impaired nutrient absorption are important pathogenicity traits in the chicken intestinal epithelium during <Emphasis Type="Italic">Campylobacter jejuni</Emphasis> colonization

Although a high number of chickens carry Campylobacter jejuni, the mechanistic action of colonization in the intestine is still poorly understood. The current study was therefore designed to investigate the effects of C. jejuni on glucose uptake, amino acids availability in digesta, and intracellular calcium [Ca²⁺]_i signaling in the intestines of broiler chickens. For this, we compared: control birds (n?=?60) and C. jejuni-infected birds (n?=?60; infected orally with 1?×?10⁸ CFU of C. jejuni NCTC 12744 at 14 days of age). Our results showed that glucose uptake was reduced due to C. jejuni infection in isolated jejunal, but not in cecal mucosa at 14 days postinfection (dpi). The decrease in intestinal glucose absorption coincided with a decrease in body weight gain during the 2-week post-infectious period. A reduction in the amount of the amino acids (serine, proline, valine, leucine, phenylalanine, arginine, histidine, and lysine) in ileal digesta of the infected birds at 2 and/or 7 dpi was found, indicating that Campylobacter utilizes amino acids as a carbon source for their multiplication. Applying the cell-permeable Ca²⁺ indicator Fluo-4 and two-photon microscopy, we revealed that [Ca²⁺]_i was increased in the jejunal and cecal mucosa of infected birds. The muscarinic agonist carbachol induced an increase in [Ca²⁺]_i in jejunum and cecum mucosa of control chickens, a response absent in the mucosa of infected chickens, demonstrating that the modulation of [Ca²⁺]_i by Campylobacter might be involved in facilitating the necessary cytoskeletal rearrangements that occur during the bacterial invasion of epithelial cells. In conclusion, this study demonstrates the multifaceted interactions of C. jejuni with the gastrointestinal mucosa of broiler chickens. For the first time, it could be shown that a Campylobacter infection could interfere with intracellular Ca²⁺ signaling and nutrient absorption in the small intestine with consequences on intestinal function, performance, and Campylobacter colonization. Altogether, these findings indicate that Campylobacter is not entirely a commensal and can be recognized as an important factor contributing to an impaired chicken gut health.     

14-O-Heterocyclic-substituted naltrexone derivatives as non-peptide mu opioid receptor selective antagonists: Design,synthesis, and biological studies

Mu opioid receptor antagonists have clinical utility and are important research tools. To develop non-peptide and highly selective mu opioid receptor antagonist, a series of 14-O-heterocyclic-substituted naltrexone derivatives were designed, synthesized, and evaluated. These compounds showed subnanomolar-to-nanomolar binding affinity for the mu opioid receptor. Among them, compound 1 exhibited the highest selectivity for the mu opioid receptor over the delta and kappa receptors. These results implicated an alternative ‘address’ domain in the extracellular loops of the mu opioid receptor.     

Predicting the unpredictable: transmission of drug-resistant HIV

We use a mathematical model to understand (from 1996 to 2001) and to predict (from 2001 to 2005) the evolution of the epidemic of drug-resistant HIV in San Francisco. We predict the evolutionary trajectories for 1,000 different drug-resistant strains with each strain having a different fitness relative to a drug-sensitive strain. We calculate that the current prevalence of resistance is high, and predict it will continue to rise. In contrast, we calculate that transmission of resistance is currently low, and predict it will remain low. We show that the epidemic of resistance is being generated mainly by the conversion of drug-sensitive cases to drug-resistant cases, and not by the transmission of resistant strains. We also show that transmission of resistant strains has not increased the overall number of new HIV infections. Our results indicate that transmission of resistant strains is, and will remain, a relatively minor public health problem.     

Transport of ketone bodies and lactate in the sheep ruminal epithelium by monocarboxylate transporter 1

Due to intensive intracellular metabolism of short-chain fatty acids, ruminal epithelial cells generate large amounts of D-beta-hydroxybutyric acid, acetoacetic acid, and lactic acid. These acids have to be extruded from the cytosol to avoid disturbances of intracellular pH (pH(i)). To evaluate acid extrusion, pH(i) was studied in cultured ruminal epithelial cells of sheep using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Extracellular addition of D-beta-hydroxybutyrate, acetoacetate, or lactate (20 mM) resulted in intracellular acidification. Vice versa, removing extracellular D-beta-hydroxybutyrate, acetoacetate, or lactate after preincubation with the respective monocarboxylate induced an increase of pH(i). Initial rate of pH(i) decrease as well as of pH(i) recovery was strongly inhibited by pCMBS (400 microM) and phloretin (20 microM). Both cultured cells and intact ruminal epithelium were tested for the possible presence of proton-linked monocarboxylate transporter (MCT) on both the mRNA and protein levels. With the use of RT-PCR, mRNA encoding for MCT1 isoform was demonstrated in cultured ruminal epithelial cells and the ruminal epithelium. Immunostaining with MCT1 antibodies intensively labeled cultured ruminal epithelial cells and cells located in the stratum basale of the ruminal epithelium. In conclusion, our data indicate that MCT1 is expressed in the stratum basale of the ruminal epithelium and may function as a main mechanism for removing ketone bodies and lactate together with H+ from the cytosol into the blood.     

Sodium glucose-linked transport in the ruminal epithelium of fallow deer – comparison to sheep

A higher expression of the sodium glucose-linked transporter, SGLT-1, has been previously demonstrated in the intestine of adult fallow deer compared to sheep. The functional presence of SGLT-1 in the rumen of both species was investigated in the present study. Isolated ruminal epithelia were incubated in Ussing chambers. D-Glucose or 3-O-methyl-alpha-D-glucose (3-OMG) were applied at 10 mmol x l-1 to the mucosal side of tissues and the changes in short-circuit current (Delta I(sc)) were recorded. Alternatively, apical uptake of [14C]-D-glucose (200 micro mol x l-1) was determined in the presence or absence of phlorizin (100 micro mol x l-1) or Na+ (115 mmol x l-1). In both species, mucosal D-glucose addition induced a larger ( P<0.05) Delta I(sc) than the mucosal addition of 3-OMG. When comparing the effects of D-glucose or 3-OMG between species, the Delta I(sc) was two-fold larger ( P<0.01) in sheep compared to fallow deer. Accordingly, phlorizin-sensitive D-glucose uptake was approximately 50% smaller ( P<0.05) in fallow deer. It is concluded that D-glucose can be absorbed via SGLT-1 from the forestomachs of both species. However, the intermediate-mixed feeding habit of fallow deer does not seem to coincide with a higher activity of the ruminal SGLT-1.