Background Glucose absorption postprandially increases markedly to levels far greater than possible by the classic glucose transporter sodium-glucose cotransporter 1 (SGLT1). Hypothesis Luminal concentrations of glucose >50 mM lead to rapid, phenotypic, non-genomic adaptations by the enterocyte to recruit another transporter, glucose transporter 2 (GLUT2), to the apical membrane to increase glucose absorption. Methods Isolated segments of jejunum were perfused in vivo with glucose-containing solutions in anesthetized rats. Carrier-mediated glucose uptake was measured in 10mM and 100 mM glucose solutions (n=6 rats, each) with and without selective inhibitors of SGLT1 and GLUT2. Results Mean rate of carrier-mediated glucose uptake increased in rats perfused with 100 mM versus 10 mM glucose to 13.9±2.9μmol from 2.1±0.1μmol, respectively (p<0.0001). Using selective inhibitors, the relative contribution of GLUT2 to glucose absorption was 56% in the 100 mM concentration of glucose compared to the 10 mM concentration (27%; p<0.01). Passive absorption accounted for 6% of total glucose absorption at 100 mM glucose. Conclusion A small amount of GLUT2 is active at the lesser luminal concentrations of glucose, but when exposed to concentrations of 100 mM, the enterocyte presumably changes its phenotype be recruiting GLUT2 apically to markedly augment glucose absorption.

INTRODUCTION Traditional models of intestinal glucose absorption confine GLUT2 to the basolateral membrane. Evidence suggests that GLUT2 is translocated to the apical membrane when the enterocyte is exposed to high luminal glucose concentrations. HYPOTHESIS GLUT2 translocates to the apical membrane by a PKC signaling mechanism dependent on activity of SGLT1 and the cellular cytostructure. METHODS Transporter-mediated glucose uptake was studied in rat jejunum using everted sleeves under 7 conditions: Control, SGLT1 inhibition (phlorizin), GLUT2 inhibition (phloretin), both SGLT1 and GLUT2 inhibition, PKC inhibition (calphostin C or chelerythrine), and disruption of cellular cytostructure (nocodazole). Each condition was tested in iso-osmotic solutions of 1, 20, or 50 mM glucose for 1 or 5 min incubations (n=6 rats each). RESULTS Control rats exhibited a saturable pattern of uptake at both durations of incubation. Phlorizin (p≤0.006 each) inhibited markedly and phloretin (p≤0.01 each) inhibited partially glucose uptake in all concentrations and time. Phloretin and phlorizin together completely inhibited uptake (p=0.004 each). Calphostin C, chelerythrine, and nocodazole had little effect on glucose uptake at either 1 or 5 min. SUMMARY Inhibition of SGLT1 led to near complete cessation of transporter-mediated glucose uptake, while GLUT2 inhibition led to partial inhibition, suggesting some constitutive expression of GLUT2 in the apical membrane. Disruption of PKC signaling or cytoskeletal integrity partially inhibited transporter-mediated glucose uptake only in 1 mM glucose, suggesting a non-specific effect. CONCLUSIONS Under these conditions, it does not appear that GLUT2 is translocated to the apical membrane on the cellular cytostructure in response to PKC signaling.

Introduction-To quantify transmembrane transport of dipeptides by PepT1, passive uptake (non-PepT1 mediated) must be subtracted from total (measured) uptake. Three methods have been described to estimate passive uptake: perform experiments at cold temperatures, inhibit target dipeptide uptake with greater concentration of a second dipeptide, or use modified MichaelisMenten kinetics. We hypothesized that performing uptake experiments at pH (8.0) would estimate passive uptake accurately, because PepT1 requires a proton gradient. Our aim was to determine the most accurate method to estimate passive uptake.

Introduction Proteins are absorbed primarily as short peptides via PepT1. Hypothesis Intestinal adaptation for peptide absorption after massive mid-small intestinal resection occurs by increased expression of PepT1 in the remnant small intestine and colon. Methods Peptide uptake was measured in duodenum, jejunum, ileum, and colon using Glycyl-Sarcosine 1 wk (n=9) and 4 wk (n=11) after 70% mid-small bowel resection, and in corresponding segments from unoperated rats (n=12) and after transection and reanastomosis of jejunum and ileum (n=8). Expression of PepT1 (mRNA, protein) and villus height were measured. Results Intestinal transection/reanastomosis did not alter gene expression. Compared to non-operated controls, 70% mid-small bowel resection increased jejunal peptide uptake (p<0.05) associated with increased villus height (1.13 vs 1.77 and 1.50 mm resp, p<0.01). In ileum although villus height increased at 1 and 4 wk (1.03 vs 1.21 and 1.35 mm resp; p<0.01), peptide uptake was not altered. PepT1 mRNA and protein were decreased at 1 wk, and PepT1 protein continued low at 4 wk. Gene expression, peptide uptake, and histomorphology were unchanged in the colon. Conclusions Jejunal adaptation for peptide absorption occurs by hyperplasia. Distal Ileum and colon do not have a substantive role in adaptation for peptide absorption.

OBJECTIVES: Barrett's esophagus (BE) is the precursor lesion and a major risk factor for esophageal adenocarcinoma (EAC). Although patients with BE undergo routine endoscopic surveillance, current screening methodologies have proven ineffective at identifying individuals at risk of EAC. Since microRNAs (miRNAs) have potential diagnostic and prognostic value as disease biomarkers, we sought to identify an miRNA signature of BE and EAC. METHODS: High-throughput sequencing of miRNAs was performed on serum and tissue biopsies from 31 patients identified either as normal, gastroesophageal reflux disease (GERD), BE, BE with low-grade dysplasia (LGD), or EAC. Logistic regression modeling of miRNA profiles with Lasso regularization was used to identify discriminating miRNA. Quantitative reverse transcription polymerase chain reaction was used to validate changes in miRNA expression using 46 formalin-fixed, paraffin-embedded specimens obtained from normal, GERD, BE, BE with LGD or HGD, and EAC subjects. RESULTS: A 3-class predictive model was able to classify tissue samples into normal, GERD/BE, or LGD/EAC classes with an accuracy of 80%. Sixteen miRNAs were identified that predicted 1 of the 3 classes. Our analysis confirmed previous reports indicating that miR-29c-3p and miR-193b-5p expressions are altered in BE and EAC and identified miR-4485-5p as a novel biomarker of esophageal dysplasia. Quantitative reverse transcription polymerase chain reaction validated 11 of 16 discriminating miRNAs. DISCUSSION: Our data provide an miRNA signature of normal, precancerous, and cancerous tissue that may stratify patients at risk of progressing to EAC. We found that serum miRNAs have a limited ability to distinguish between disease states, thus limiting their potential utility in early disease detection.