Which statement best describes the in vitro model used to study intestinal permeability and absorption for orally administered drugs?

• A. Caco-2 cell monolayers model intestinal absorption
• B. Hepatocytes model renal filtration
• C. Renal tubule cells model hepatic metabolism
• D. Fibroblasts model gastric emptying

Answer: (A)

The main concept being tested is that Caco-2 cell monolayers are the standard in vitro model for studying intestinal permeability and drug absorption. When grown as a polarized monolayer on Transwell inserts, Caco-2 cells differentiate into enterocyte-like cells with tight junctions and apical-basolateral polarity, creating a barrier that mimics the intestinal lining. This setup allows researchers to measure how a compound crosses the intestinal epithelium and to assess whether transporters influence its movement, typically expressed as apparent permeability (Papp). Because it directly represents the barrier the drug must traverse after oral administration, this model best describes intestinal permeability and absorption. Other options correspond to different organs or processes—hepatocytes focus on liver metabolism, renal tubule cells on kidney filtration, and fibroblasts do not model the intestinal barrier or gastric emptying.