Penetration and binding of aldose-reductase inhibitors in the lens

Diffusion, partitioning, and binding of two aldose-reductase inhibitors (ARI) in the rat lens were investigated under in vitro conditions. A lipophilic ARI (CT-112) and a hydrophilic ARI (AD-5467) were used as model drugs. Under lens-uptake conditions, the drug concentration in the lens increased rapidly during the initial 10 hr and reached steady state (equilibrium) after 24 hr. Despite the equilibrium concentration of CT-112 in the lens which is approximately three times of that of AD-5467, the inhibition rate of CT-112 against the accumulation of sugar alcohols was appreciably lower than that for AD-5467. The equilibrium concentration in the lens after the penetration/binding experiment also suggested that AD-5467 may interact with the target sites of enzymes more than that for CT-112. The time course of the lens concentration during the uptake and desorption experiments was well described by a diffusion/binding model assuming a Langmuir binding. The diffusion coefficient, the partition coefficient, and binding parameters in the rat lens were determined for the two ARIs.