Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

Contrast-enhancing magnetic resonance imaging with the liver-specific agent gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) has been shown to improve the detection rate of focal lesions. There is evidence from preclinical studies that multidrug organic anion transporters are involved in hepatic uptake of Gd-EOB-DTPA. Therefore, we evaluated affinity of the contrast agent to human organic anion-transporting polypeptides (OATP1B1, OATP1B3, OATP2B1) and to the Na⁺/taurocholate cotransporting polypeptide (NTCP) using stable transfected human embryonic kidney (HEK) 293 cells. In competition assays, Gd-EOB-DTPA inhibited the uptake of bromosulfophthalein (BSP) by OATP1B1 (IC₅₀ = 0.6 mM) and OATP1B3 (IC₅₀ = 0.4 mM). In comparison, the IC₅₀ values for rifampicin were 11.9 (OATP1B1), 1.4 (OATP1B3), and 80.5 μM (OATP2B1), respectively. Uptake of BSP by OATP2B1, uptake of taurocholic acid by NTCP, and viability of all HEK cells were not influenced by Gd-EOB-DTPA in concentrations up to 10 mM. In uptake assays using a new liquid chromatography-tandem mass spectrometry method for quantification, Gd-EOB-DTPA was a substrate for OATP1B1 (K_m = 0.7 mM, V_max = 10.5 pmol/mg × min), OATP1B3 (K_m = 4.1 mM, V_max = 22.7 pmol/mg × min), and NTCP (K_m = 0.04 mM, V_max = 1.4 pmol/mg × min). The uptake by OATP2B1 was not different from the vector control. In conclusion, Gd-EOB-DTPA is a substrate of the liver-specific OATP1B1, OATP1B3, and NTCP.

Oral administration is the most common route of drug delivery. The absorption of a drug from the gut into the bloodstream involves disintegration of the solid dosage form, dissolution of the active pharmaceutical ingredient and its transport across the gut wall. The efficiency of these processes is determined by highly complex and dynamic interplay between the gastrointestinal tract, the dosage form and the API. The European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) aims to improve our understanding of intestinal drug absorption by creating a multidisciplinary Network of researchers from academia and industry engaging in scientific discussions. As part of the basis for the UNGAP project, this review aims to summarize the current knowledge on anatomy and physiology of the human gastrointestinal tract with emphasis on human studies for the evaluation of the regional drug absorption and the prediction of oral dosage form performance. A range of factors and methods will be considered, including imaging methods, intraluminal sampling and, models for predicting segmental/regional absorption. In addition, in vitro and in silico methods to evaluate regional drug absorption will be discussed. This will provide the basis for further work on improving predictions for the in vivo behavior of drug products in the gastrointestinal tract.