A method for the determination of cellular permeability coefficients and aqueous boundary layer thickness in monolayers of intestinal epithelial ( Caco-2) cells grown in permeable filter chambers

Abstract

A linear relationship between apparent permeability coefficients ( P app) and agitation rate was used to determine cell permeability coefficients ( P c) and the thickness of the aqueous boundary layer ( h aq) in monolayers of Caco-2 cells. Drugs with different physical/chemical properties were studied. P app values for ‘highly permeable drugs’ (testosterone, corticosterone, propranolol, metoprolol, warfarin) were dependent on the agitation rate, i.e. on the h aq. The permeation of testosterone was studied in detail. In the absence of agitation, the measured P app value of testosterone was 35.7 ± 3.3 × 10 −63 cm/s while the P c value was 137.4 ± 8.1 X 10 −6 cm/s, i.e. 3.8 times higher. P app values for ‘less permeable drugs’ (hydrocortisone, salicylic acid, sulphasalazine, mannitol) were not dependent on the agitation conditions. In the absence of agitation, h aq for testosterone was 1544 ± 142 μm and the contribution of the resistance of the aqueous boundary layer to the total diffusional resistance was 70%. h aq was reduced to 128 + 10 μm when the highest agitation rate was used. Under these conditions, the contributions of the resistances of the aqueous boundary layer and the Caco-2 cell monolayers were 16 and 73%, respectively. Similar results were obtained for the other highly permeable drugs. The results indicate that the P app values for highly permeable drugs are controlled not only by the aqueous boundary layer but also by the Caco-2 cell monolayers.