Targeted drug delivery to absorptive epithelia by receptor-mediated endocytosis has emerged as a prominent means to
Fosbretabulin cost improve oral delivery of drugs . Vitamins as ligands, which can specifically bind to enterocytic receptors, have been extensively studied for the oral delivery of poorly permeable molecules [18–22]. Biotin receptors that distribute in the small intestine and this website partially in the colon are responsible for the essential absorption of biotin by nonspecific receptor-mediated endocytosis . Additionally, biotin plays an important role in maintaining the homeostasis of blood glucose . Improved cellular permeability and higher hypoglycemic effect after oral administration of biotin-conjugated Pevonedistat concentration glucagon-like peptide-1 has been observed . Biotin-modified vehicles have been investigated for nonparenteral delivery of active ingredients [26–29]. Our previous report has also proved that biotin-modified liposomes (BLPs) have ability to improve the oral delivery of insulin, and studied the uptake and transport mechanisms in the gastrointestinal tract . However, particular enhanced absorption mechanisms and cytotoxicity of BLPs are not clear enough. Herein, we performed several experiments to further probe the oral absorption mechanism of BLPs based on previous studies  as well
as the cytotoxicity thereof. We evaluated hypoglycemic effects of BLPs of various particles, or with different amounts of biotin-DSPE using normal rats.
Meanwhile, the influence of BLPs on tight junctions and internalization process was further investigated Y-27632 2HCl by Caco-2 cells. Methods Materials Porcine insulin (29 IU/mg) was provided by Jiangsu Wanbang Biochemical Pharmaceutical Co, Ltd (Xuzhou, China). Soybean phosphatidylcholine (SPC, Lipoid S75), cholesterol (CH), and 1, 2-distearoyl-sn-glycero-3-phosphatidyl ethanolamine (DSPE) were supplied by Lipoid (Ludwigshafen, Germany). Fluorescein isothiocyanate (FITC) and biotin were purchased from Sigma (Shanghai, China). Sephadex G-50 was obtained from Pharmacia (Shanghai, China). Deionized water was prepared by a Milli-Q purification system (Molsheim, France). HPLC-grade acetonitrile was provided by Merck (Darmstadt, Germany). All other chemicals were of analytical grade and used as received. Preparation of BLPs SPC, biotin-DSPE (synthesized according to previous report ), and cholesterol were dissolved in absolute ether to prepare the organic phase, into which the aqueous phase, insulin citric acid-Na2HPO4 buffer solution (pH 4.0, if not specified otherwise), was added dropwise following ultra-sonication to prepare the W/O emulsion. The organic solvent in the emulsion was then evaporated toward a rota-evaporator under 0.05- to 0.06-MPa pressure at a rotating speed of 50 rpm at 30°C until glutinous gel formed. Afterwards, citric acid-Na2HPO4 buffer with pH 3.8 was instilled to hydrate the lipidic gel until a homogeneous dispersion was formed.