Yoko Taki

Analysis of Drug Permeation Across Caco-2 Monolayer: Implication for Predicting In Vivo Drug Absorption

AbstractPurpose. The aim of the present work is to characterize in vitro drug permeation processes across Caco-2 monolayer and to identify the advantages of this cultured cell system in predicting in vivo drug absorption after oral administration. Methods. The passive permeability of various drugs through Caco-2 monolayer was measured using Ussing-type chambers and compared with that of the isolated rat jejunum and colon. The in vivo drug permeability to the intestinal membrane was estimated by means of an intestinal perfusion study using the rat jejunum. Results. In Caco-2 monolayer, drug permeability increased with increasing drug lipophilicity and showed a good linear relationship with the in vivo permeability. In contrast, in the isolated jejunum and colon, the permeability of high lipophilic drugs was almost constant and, propranolol, a drug with the highest lipophilicity, hardly passed through the jejunal membrane in vitro. As a result, there was no significant relationship between in vitro and in vivo drug permeability in rat jejunum. However, the amount of drugs accumulated in the jejunal mucosa increased with increasing drug lipophilicity even under the in vitro condition. Conclusions. The permeation and the accumulation studies suggested that the rate-limiting process of in vitro permeation of lipophilic drugs through the intestinal membrane differs from that of in vivo drug absorption. On the other hand, drug permeation through Caco-2 monolayer, which consists of an epithelial cell layer and a supporting filter, is essentially the same process as that of in vivo drug absorption. We concluded that the simple monolayer structure of a cultured cell system provides a distinct advantage in predicting in vivo drug absorption.

Direct Drug Transport from the Rat Nasal Cavity to the Cerebrospinal Fluid: the Relation to the Molecular Weight of Drugs

To clarify the relationship between the direct transport from the rat nasal cavity to the cerebrospinal fluid (CSF) and the molecular weight of the drug, the transport of fluorescein isothiocyanate‐labelled dextran (FD) with various molecular weights was investigated. FDs (average molecular weights 4400 (FD4); 9400 (FD10); 18 900 (FD20); 40 500 Da (FD40)) were administered nasally or intravenously to rats, and the concentrations in the plasma and the CSF were measured and compared.

Characterization of Drug Transport Through Tight-Junctional Pathway in Caco-2 Monolayer: Comparison with Isolated Rat Jejunum and Colon

Drug transport through the tight-junctional pathway in Caco-2 monolayer was studied by examining the relationship between its permeability to hydrophilic drugs and membrane conductance. Compared with the rat isolated jejunum or colon, Caco-2 monolayer displayed high electrical resistance and low conductance, as well as low permeability to sulfanilic acid and FITC-dextran (M.W. 4000). However, there was a linear relationship between the drug permeability and partial Cl− ion conductance for Caco-2 monolayer, rat jejunum and colon. Hence, the permeability to those drugs per unit of Cl− conductance is similar in the three membranes, suggesting that the size (radius) of the tight-junctional pathway in the three membranes is similar. In addition, when the electrical resistance of Caco-2 monolayer was reduced to the same level as that of the jejunum or colon by pretreatment with disodium ethylenediamine-tetraacetate, its permeability to FITC-dextran became significantly higher than that of other membranes. Accordingly, the high resistance and the low permeability of Caco-2 monolayer compared with rat intestinal membrane may be due to structural differences between the membranes, rather than a difference in the tightness of the junction.

Kinetic Analysis of the Drug Permeation Process Across the Intestinal Epithelium

The rat intestinal lumen and the blood vessel were simultaneously perfused to study drug permeation across the intestinal epithelium. On the basis of drug disappearance from the intestinal lumen and its appearance into the vascular outflow, the mean time required for permeation across the intestinal membrane (MPT) and the permeation clearance (CLp) were calculated. MPT values of water, antipyrine, propranolol, imipramine and mannitol, varied from 0.45 min to 9.91 min depending on their physicochemical property. From both MPT and CLp, five drugs were classified as being (i) highly and rapidly absorbed (water, antipyrine), (ii) highly but slowly absorbed (propranolol, imipramine) and (iii) low and slowly absorbed (mannitol). Permeation profiles of these drugs were analyzed based on the diffusion model which defined the parameter for each permeation process, i.e. partitioning to and diffusion through the epithelium and clearance into the blood flow. Propranolol and imipramine partitioned into the membrane at a higher level than the other drugs. However, the clearance of both drugs from the epithelium was extremely slow, suggesting that this process is the rate-limiting step in their permeation. On the other hand, the rate-limiting step in the permeation of water and antipyrine was found to be the diffusion process in the epithelial layer.

First-pass metabolism of peptide drugs in rat perfused liver

To elucidate the extent and mechanisms of the first‐pass metabolism of peptide drugs in the liver after oral administration, a liver perfusion study was performed in rats using metkephamid, a stable analogue of methionine enkephalin, and thyrotropin‐releasing hormone (TRH), as model peptides.