A physiological approach for preparing and conducting intestinal bioavailability studies using experimental systems

Various in vitro models, such as digestion procedures, element dialysis across membranes and also the Caco-2 cellular absorptive system, are currently used to study intestinal nutrient bioavailability. These systems were established as an alternative to human and animal studies. The principle requirement for successfully performing such kinds of experimental studies is to achieve conditions, which are similar to in vivo conditions. Therefore, it is absolutely necessary to consider the natural environment in the human gut. Consequently, in vitro studies should be prepared and conducted according to evidence-based gastrointestinal physiology. This concise review summarizes important processes in the human intestine, like peptic and pancreatic digestion, adjustment of pH, peristaltic frequency, osmolality, composition of the serosal (= acceptor) solution, and permeability characteristics of the enterocyte monolayer, which are relevant for bioavailability studies using in vitro models.