Electrogenic ion transport in duodenal biopsies from children with coeliac disease

Oral drug absorption in pediatrics: the intestinal wall, its developmental changes and current tools for predictions

The dissolution, intestinal absorption and presystemic metabolism of a drug depend on its physicochemical characteristics but also on numerous physiological (e.g. gastrointestinal pH, volume, transit time, morphology) and biochemical factors (e.g. luminal enzymes and flora, intestinal wall enzymes and transporters). Over the past decade, evidence has accumulated indicating that these factors may differ in children and adults resulting in age-related changes in drug exposure and drug response. Thus, drug dosage may require adjustment for the pediatric population to ensure the desired therapeutic outcome and to avoid side-effects. Although tremendous progress has been made in understanding the effects of age on intestinal physiology and function, significant knowledge gaps remain. Studying and predicting pharmacokinetics in pediatric patients remains challenging due to ethical concerns associated with clinical trials in this vulnerable population, and because of the paucity of predictive in vitro and in vivo animal assays. This review details the current knowledge related to developmental changes determining intestinal drug absorption and pre-systemic metabolism. Supporting experimental approaches as well as physiologically based pharmacokinetic modeling are also discussed together with their limitations and challenges. Copyright © 2016 John Wiley & Sons, Ltd.

Transglutaminase 2-specific coeliac disease autoantibodies induce morphological changes and signs of inflammation in the small-bowel mucosa of mice

Coeliac disease is hallmarked by an abnormal immune reaction against ingested wheat-, rye- and barley-derived gluten and the presence of transglutaminase 2 (TG2)-targeted autoantibodies. The small-bowel mucosal damage characteristic of the disorder develops gradually from normal villus morphology to inflammation and finally to villus atrophy with crypt hyperplasia. Patients with early-stage coeliac disease have TG2-autoantibodies present in serum and small-intestinal mucosa and they may already suffer from abdominal symptoms before the development of villus atrophy. Previously, we have shown that intraperitoneal injections of coeliac patient-derived sera or purified immunoglobulin fraction into mice induce a condition mimicking early-stage coeliac disease. In the current study, we sought to establish whether recombinantly produced patient-derived TG2-targeted autoantibodies are by themselves sufficient for the development of such an experimentally induced condition in immune-compromised mice. Interestingly, mice injected with coeliac patient TG2-antibodies had altered small-intestinal mucosal morphology, increased lamina propria cellular infiltration and disease-specific autoantibodies deposited in the small bowel, but did not evince clinical features of the disease. Thus, coeliac patient-derived TG2-specific autoantibodies seem to be sufficient for the induction of subtle small-bowel mucosal alterations in mice, but the development of clinical features probably requires additional factors such as other antibody populations relevant in coeliac disease.

Epithelial electrical resistance as a measure of permeability changes in pediatric duodenal biopsies

OBJECTIVES

Intestinal permeability measured with medium-sized oral probes is increased in cystic fibrosis (CF) and celiac disease (CD), probably reflecting reduced tight junction resistance. The aim of this study was to evaluate whether square-pulse analysis of duodenal biopsies from children can be used to determine electrical tight junction resistance.

METHODS

Intestinal biopsies from children with different stages of CD and from patients with CF were studied in a modified Ussing chamber. The epithelium was assumed to act as an electrical circuit consisting of a current generator parallel with a resistance and a capacitance. Subepithelial and epithelial resistances were determined by square-pulse analysis, and the generated current was calculated.

RESULTS

Confirming data using permeability probes, reduced epithelial electrical resistance was found both in patients with CF and CD. Only the CF patients had reduced resting current as well. The secretagogues prostaglandin E2, cyclic adenosine monophosphate and acetylcholine increased the current in both control biopsies and biopsies with villous atrophy but had no significant effect on epithelial resistance.

CONCLUSIONS

Measurement of electrical resistance in duodenal biopsies can be used as an alternative method of quantifying permeability in pediatric biopsies.

Abnormal fatty acid pattern in intestinal mucosa of children with celiac disease is not reflected in serum phospholipids

OBJECTIVE

Celiac disease (CD) is characterized by chronic inflammation of the small intestinal mucosa with disturbed epithelial transport. The fatty acid (FA) composition of intestinal membranes is important for epithelial function, and disturbances may contribute to the pathophysiology of the disease. We aimed to evaluate whether the intestinal mucosal FA status was reflected in serum phospholipids of patients with CD.

PATIENTS AND METHODS

Samples were obtained from 7 pediatric patients with active CD showing mucosal atrophy, 6 pediatric patients with CD in remission, and 11 control pediatric patients with morphologically healthy intestinal mucosa. Small intestinal biopsies were obtained using a Watson biopsy capsule under fluoroscopic control. Blood samples were collected on the same morning after an overnight fast. Tissue phospholipids were isolated by high-performance liquid chromatography, and FAs were analyzed by capillary gas-liquid chromatography.

RESULTS

Serum phospholipid FA showed marginal differences between the patients with CD and the controls. Significant differences were observed in mucosa with active CD compared with controls. Linoleic acid (18:2n-6) level was decreased, whereas those of its derivatives were elevated, indicating increased transformation of n-6 FA. Mead acid (20:3n-9) level was increased, with an increased ratio of Mead acid to arachidonic acid (20:4n-6) levels, suggesting essential fatty acid deficiency. The n-3 FA levels were not significantly changed. During remission, the FA pattern of the intestinal mucosa was mainly similar to that in controls.

CONCLUSIONS

The FA abnormality of intestinal mucosa in patients with active CD was not reflected in serum values. Altered FA content may contribute to the pathophysiology of the disease because FAs are important for enzymes and for the transport and receptor functions of epithelial membranes.

Endoscopic biopsies in Ussing chambers evaluated for studies of macromolecular permeability in the human colon

OBJECTIVE

Studies of mucosal permeability to protein antigens in humans are limited to in vitro techniques. The use of surgical specimens for such studies has major shortcomings. Endoscopic biopsies in Ussing chambers have been introduced as a means of studying secretion and transepithelial permeability, but have not been evaluated for studies of protein antigen uptake in human intestine.

MATERIAL AND METHODS

Standard forceps biopsies from the sigmoid colon of 24 healthy volunteers were mounted in Ussing chambers with an exposed tissue area of 1.76 mm2. 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP; 45 kDa protein antigen) were used as permeability markers. Mucosal permeability, electrophysiology, histology and energy contents of the biopsies were studied over time. To evaluate the ability of the technique to detect permeability changes, the mucosa was modulated with capric acid, a medium-chain fatty acid, known to affect tight junctions.

RESULTS

In the Ussing chamber the mucosal biopsies were viable for 160 min with stable levels of ATP and lactate, and only minor changes in morphology. Steady-state permeability with low variability was seen for both markers during the 30-90 min period. Exposure to capric acid induced a rapid decrease in short-circuit current (Isc) and a slower reversible decrease in transepithelial resistance (TER), as well as an increased permeability to 51Cr-EDTA and HRP.

CONCLUSIONS

Endoscopic biopsies of human colon are viable in Ussing chambers and are reliable tools for studies of mucosal permeability to protein antigens. The technique offers a broad potential for studies of mucosal function in the pathophysiology of human gastrointestinal diseases.

Cysteinyl leukotrienes are secretagogues in atrophic coeliac and in normal duodenal mucosa of children

OBJECTIVE

The pathophysiology of intestinal inflammation and diarrhoea is complex and involves the arachidonic acid cascade. Prostaglandins induce chloride secretion in healthy subjects and in patients with coeliac disease. Leukotrienes (LTs) are also known inflammatory mediators which have been shown to stimulate ion secretion in ileum and colon of rats and rabbits. The aim of this study was to determine the effects of leukotrienes C(4) (LTC(4)) and D(4) (LTD(4)) in normal and atrophic intestinal mucosa in children.

MATERIAL AND METHODS

Routine paediatric intestinal biopsies were obtained from 109 children. Sixty-seven control biopsies and 42 biopsies from children with different stages of coeliac disease were mounted in a modified Ussing chamber. Potential difference (Pd) was measured continuously and tissue resistance (R(t)) and the generated current (I(m)) were calculated.

RESULTS

In morphologically normal mucosa of duodenum, LTC(4) and LTD(4) increased Pd and I(m) in a dose-dependent manner. The increase was more pronounced in the distal than in the proximal part, similar to the response to prostaglandin E(2). The induced current was chloride-mediated, since replacement of Cl(-) with SO(4)(2-) in the bathing solution eliminated the response to the LTs. The LTC(4)-induced secretion was significantly decreased in atrophic mucosa, but the response was partially restored after preincubation with the cyclooxygenase inhibitor indomethacin.

CONCLUSIONS

The results showed that LTC(4) and LTD(4) are secretagogues in the duodenal mucosa from healthy children by inducing a net chloride secretion. Restoration of the response in coeliac disease by cyclooxygenase inhibition suggests interactions between the different pathways of the arachidonic cascade in the intestinal mucosa.

Effects of dietary lectins on ion transport in epithelia

Phytohemagglutinins are widely distributed in common food items. They constitute a heterogeneous group of proteins, which are often resistant to proteolysis in the gastrointestinal tract. Upon binding to the luminal membrane of intestinal cells, they can interfere with digestive, protective or secretory functions of the intestine. Phytohemagglutinins present in red kidney beans and jackbeans have been shown to induce diarrhea and hypersecretion in human airways, but the underlying mechanisms remain obscure. We examined how agglutinins from wheat germ (WGA), soy bean (SBA), red kidney beans (Pha-E, Pha-L), and jackbeans (Con-A) affect ion transport in mouse airways and large intestine using Ussing chamber techniques. We found that Pha-E, Pha-L, and Con-A but not WGA and SBA inhibit electrogenic Na(+) absorption dose dependently in both colon and trachea. The inhibitory effects of Con-A on Na(+) absorption were suppressed by the sugar mannose, by inhibition of phospholipase C (PLC) and protein kinase C (PKC). Thus, nutritional phytohemagglutinins block salt absorption in a PLC- and PKC-dependent manner, probably by inhibition of the epithelial Na(+) channel (ENaC). This effect may be therapeutically useful in patients suffering from cystic fibrosis.