This work provides an elaborate characterization of human intestinal fluids (HIF) collected in fasted- and fed-state conditions. HIF from 20 healthy volunteers (10 M/F) were aspirated by intubation near the ligament of Treitz in a time-dependent manner (10-min intervals) and characterized for pH, bile salts, phospholipids, cholesterol, triacylglycerides (TAG), diacylglycerides (DAG), monoacylglycerides (MAG), free fatty acids (FFA), pancreatic lipase, phospholipase A2, and nonspecific esterase activity. For almost all parameters, a food-induced effect was observed. Results were characterized by a high variability, as illustrated by the broad ranges observed for each parameter: pH (fasted: 3.4-8.3; fed: 4.7-7.1), bile salts (fasted: 0.03-36.18 mM; fed: 0.74-86.14 mM), phospholipids (fasted: 0.01-6.33 mM; fed: 0.16-14.39 mM), cholesterol (fasted: 0-0.48 mM; fed: 0-3.29 mM), TAG (fed: 0-6.76 mg/mL), DAG (fed: 0-3.64 mg/mL), MAG (fasted: 0-1.09 mg/mL; fed: 0-11.36 mg/mL), FFA (fasted: 0-3.86 mg/mL; fed: 0.53-15.0 mg/mL), pancreatic lipase (fasted: 26-86 g/mL; fed: 146-415 g/mL), phospholipase A2 (fasted: 3-6 ng/mL; fed: 4.3-27.7 ng/mL), and nonspecific esterase activity (fasted: 270-4900 U/mL; fed: 430-4655 U/mL). This comprehensive overview may serve as reference data for physiologically based pharmacokinetic modeling and the optimization of biorelevant simulated intestinal fluids for the use in in vitro dissolution, solubility, and permeability profiling.

Intestinal fluids dictate the intraluminal environment, and therefore, they substantially affect the absorption of orally taken drugs. The characterization of human intestinal fluids (HIF) and the design of simulated intestinal fluids (SIF) mainly focus on composition, not necessarily taking into account the ultrastructure of HIF. Colloidal structures in HIF and SIF can enhance the solubilizing capacity for lipophilic drugs while decreasing the bioaccessible fraction. As such, colloids present in HIF play a crucial role and require an in-depth characterization. Therefore, the present study pursued a comprehensive characterization of the ultrastructure of fasted and fed state HIF, focusing on (i) intersubject variability in relation to composition and (ii) differences between the ultrastructure of HIF and SIF. Individual as well as pooled HIF were collected from human volunteers near the ligament of Treitz and compositionally characterized previously. A HIF population pool (20 healthy volunteers) for both fasted (FaHIF) and fed state (FeHIF) was compared to current SIF, as well as selected HIF from different individuals. The selected individual HIF represented the full spectrum of compositional characteristics. Three complementary electron microscopy techniques, cryo-TEM (transmission electron microscopy), negative stain TEM, and cryo-SEM (scanning electron microscopy), were employed to provide a comprehensive view of the colloidal structures in HIF and SIF. The use of complementary EM techniques provided a unique insight into the ultrastructure of HIF, including their native conformation. These characterizations showed that FaHIF and FaSSIF (fasted state simulated intestinal fluids) only consist of (mixed)-micelles with minimal intersubject variability. Ultrastructures in FeSSIF (fed state simulated intestinal fluids) and FeSSIF-v2 are not representative of the colloids in FeHIF since SIF lack (multi)-lamellar vesicles and lipid droplets. Furthermore, the images demonstrated significant intersubject variability in the ultrastructure of FeHIF, which may contribute to variable absorption of lipophilic drugs.

Background: Functional dyspepsia is a common functional gastrointestinal disorder in which a variety of pathophysiological mechanisms such as increased intestinal permeability and low-grade inflammation are involved. The factor causing these alterations, however, has not been identified. Objective: We aimed to evaluate the luminal bile salt content and receptor expression in patients with functional dyspepsia and healthy volunteers. Methods: Gastroduodenoscopy was performed to obtain duodenal biopsies from 25 healthy volunteers and 25 patients with functional dyspepsia (Rome III) to measure duodenal bile salt receptor expression with Western blot. Duodenal fluid aspirates were collected at fixed time points during fasted and fed state conditions and bile salt composition analysis was performed by liquid chromatography-mass spectrometry/mass spectrometry. Results: Patients (N ¼ 17) displayed decreased fasted bile salt concentrations compared to healthy volunteers (N ¼ 20) over time (1.8 AE 0.3 mM vs 3.6 AE 0.5 mM; p ¼ 0.03). In addition, an increased expression of duodenal bile salt sensor vitamin D receptor was found in patients (3.7 AE 1.0-fold; p < 0.0005; N ¼ 24 for both groups). Conclusion: Patients with functional dyspepsia are characterized by a decreased duodenal bile salt concentration in fasted state and an increased duodenal vitamin D receptor expression.

Background: Functional dyspepsia (FD) is a complex disorder, in which multiple mechanisms underlie symptom generation, including impaired duodenal barrier function. Moreover, an altered duodenal bile salt pool was recently discovered in patients with FD. We aimed to evaluate the relationship between bile salts, bacterial translocation, and duodenal mucosal permeability in FD. Methods: Duodenal biopsies from patients with FD and healthy volunteers (HV)were mounted in Ussing chambers to measure mucosal resistance and bacterial passage in the absence and presence of fluorescein-conjugated Escherichia coli and glyco-ursodeoxycholic acid (GUDCA) exposure. In parallel, duodenal fluid aspirates were collected from patients and bile salts were analyzed. Key results: The transepithelial electrical resistance of duodenal biopsies from patients was lower compared with HV (21.4 ± 1.3 Ω.cm 2 vs. 24.4 ± 1.2 Ω.cm 2 ; P = .02; N = 21). The ratio of glyco-cholic and glyco-chenodeoxycholic acid (GCDCA) to tauro-and GUDCA correlated positively with transepithelial electrical resistance in patients. Glyco-ursodeoxycholic acid slightly altered the mucosal resistance, resulting in similar values between patient and healthy biopsies (22.1 ± 1.0 Ω.cm 2 vs. 23.0 ± 1.0 Ω.cm 2 ; P = .5). Bacterial passage after 120 minutes was lower for patient than for healthy biopsies (0.0 [0.0-681.8] vs. 1684.0 [0.0-4773.0] E coli units; P = .02). Glyco-ursodeoxycholic acid increased bacterial passage in patient biopsies (102.1 [0.0-733.0] vs. 638.9 [280.6-2124.0] E coli units; P = .009). No correlation was found between mucosal resistance and bacterial passage.

To date, the Caco-2 model is considered as the gold standard to predict intestinal drug absorption. Often, aqueous phosphate buffers are used as apical medium. The purpose of this study was to use fasted state human intestinal fluid (FaHIF) as apical solvent system to generate biorelevant permeability values for a series of 16 model drugs that can be used as reference data to critically evaluate fasted state simulated intestinal fluid (FaSSIF) as possible substitute medium. Caco-2 compatibility with FaHIF was achieved when 50mg/ml mucus was applied on top of the cells before adding the apical medium. The use of FaHIF as solvent system generated a broad range of apparent permeability values (Papp) for the series of model compounds. When Papp values obtained with FaHIF were compared to those obtained with FaSSIF, a strong correlation was observed (R=0.951). The use of FaSSIF in the absence of mucus did not significantly alter this correlation. For FaHIF, FaSSIF and reference phosphate buffer blank FaSSIF, a strong sigmoidal relationship was found between Papp and fahuman, illustrated by correlation coefficients of 0.961, 0.893 and 0.868, respectively. In terms of inter-subject variability, the use of FaHIF from different volunteers originating from two distinct age groups (18-25 years; 65-72 years) exhibited an average coefficient of variance (CV) of 30%. However, no age dependency in permeability could be observed. In conclusion, the data generated in this article justify the use of FaSSIF as biorelevant apical medium in the Caco-2 assay to accurately predict in vivo drug absorption. Also, the optimized mucus-containing Caco-2 model can be used in combination with intestinal fluid samples aspirated after drug administration to further investigate intraluminal drug and formulation behavior.