Ne, hydrocortisone, selenium, and o-phosphorylethanolamine; and is reconstituted in 5 ml dH2O (stock solution). Entero-STIM is a serum-free defined medium (DMEM) containing butyric acid. Butyric acid induces differentiation of intestinal epithelial cells in vitro (by downregulating c-myc expression) 18].Materials and Methods MaterialsFITC-labeled bovine insulin, sulforhodamine B, and bovine insulin were obtained from Sigma Aldrich (St. Louis, MO, USA). Salmon Calcitonin was obtained from Anaspec, Inc. (Fremont, CA, USA). Exenatide (Exendin-4) was obtained from Tocris Biosciences (Minneapolis, MN, USA). The transwell Caco-2 system was set up by using 24 well BD-BiocoatTM HTS Caco-2 assay system (fibrillar collagen coated, 1 mm pore size) obtained from BD Biosciences (Bedford, MA, USA). ELISA kits for analysis of different peptides were obtained from various commercial vendors. Bovine insulin ELISA kit was obtained from Mercodia, Inc. (Winston Salem, NC, USA). Extraction-free salmon Calcitonin and 23727046 exenatide ELISA kits were obtained from Bachem Americas, Inc. (Torrance, CA, USA). Supplies for Caco-2 culture were obtained from Fisher Scientific (Pittsburgh, PA, USA). All the ELISA kits used for the quantification analyses were peptidespecific, and were unlikely to pick any cross-reactive peptide and/ or degraded peptide fragments.Transepithelial Electrical Resistance (TEER) MeasurementsThe integrity of Caco-2 monolayer was determined by measuring the transepithelial electrical resistance (TEER) of the cell monolayer grown on filter supports using Millicell-ERS electrical resistance measuring system (Millipore, Bedford, MA) using chopstick electrodes. Briefly, the Caco-2 inserts were transferred to a 24-well culture plate with 1400 ml medium in the feeding well, and 500 ml in culture inserts. The electrodes were immersed in a way that shorter electrode was in the insert and longer electrode in the outer well. Care was taken that the electrode did not touch the monolayer. Based on the literature, a resistance reading of 150?00 V.cm2 was considered as indicative of a confluent Caco-2 monolayer with tight junctions. Precautions were while taking TEER measurements throughout the experiment to avoid cross contamination and loss of Active Pharmaceutical Ingredient (API). The electrodes of the TEER probe were thoroughly rinsed with 70 ethanol before the start of each experiment, and also after each measurement from each individual well. At the same time, the probe was gently tapped to the side walls of the transwells to avoid any possible loss of API. For all the samples withdrawn from the basolateral side, equivalent amount of fresh release medium was added, and was accounted for while calculating cumulative transport.Caco-2 Cell CultureHuman colorectal adenocarcinoma Caco-2 cell line (HTB-37) obtained from American Type culture Collection (ATCC) (Manassas, VA, USA) was used for all experiments. Cell lines were maintained as per the provider’s protocol. Cell culture was performed in HycloneH DMEM high glucose medium (Thermo Fisher Scientific, Pittsburgh, PA, USA) supplemented with 50 IU/ ml of penicillin, 50 mg/L of streptomycin, and 100 ml/L of fetal bovine serum at 37uC in a humidity-controlled 5 CO2 cell culture incubator. Cells were split at a ratio of 1:3 after reaching 90 confluence. All transwell experiments were performed with cells between 5th?4th passages due to possible phenotypic differences between cells from high and low passage i.