Hydrolysis of Prednisolone Succinate by Esterase in Rabbit Ocular Tissue

Abstract

Prednisolone concentrations in serum after both subconjunctival and intravenous injections of prednisolone sodium succinate at a 1 mg/kg equivalent dose of prednisolone in rabbits were analyzed by regularly phased high-performance liquid chromatography. The systemic availability after subconjunctival injection was determined to be almost 1.0 by comparing areas under the serum concentration-time curves for both administration routes. The initial hydrolytic rate of prednisolone succinate ester was dependent on the amount of total protein in ocular tissue homogenates and fluids as well as that in serum. The rate followed Michaelis-Menten kinetics, with an almost consistent Michaelis constant. Although the maximum hydrolytic rate per unit amount of tissue protein was the highest in conjunctival tissue, followed by corneal tissue and serum, the esterase activity corrected by total protein in the whole rabbit body should be the highest in serum, followed by conjunctival tissue. These results indicate that prednisolone sodium succinate administered subconjunctivally is hydrolized rapidly by esterase and absorbed almost completely into the systemic circulation.

Intraocular Penetration Kinetics of Prednisolone after Subconjunctival Injection in Rabbits

“…However, it has not yet been under stood, in quantitative terms, by what kind of kinetic mechanism such steroids move from the subconjunctival injection site to the var ious tissues. Our previous study [8] demon strated that the value of the area under the serum concentration-time curve of prednis olone after subconjunctival injection of its succinate ester in rabbits was almost the same as that after intravenous administra tion of the same dose. This result demon strated that prednisolone administered subconjunctivally is absorbed almost com pletely into the systemic circulation, with a half-life of 38 min, and suggested that only a small amount of prednisolone is available to the ocular tissues.…”

“…120, 240, and 360 min after injection for the 10 ntg/kg dose and 10, 60, 120, and 240 min after injection for the 0.1 mg/kg dose. At the end of each period, after sampling aqueous humor in the manner described previously [8], the animal was sacrificed via rapid injection of approximately 30 ml of air into the mar ginal vein. Following the sacrifice of each animal, approximately 700 mg of the conjunctival membrane covering the area of the injection site and both whole eyeballs was removed.…”

“…Cornea and vitreous humor were removed from frozen eyeballs. Samples for analysis by high-performance liquid chromatography were prepared in the manner de scribed previously [8], Four to nine rabbits were used for each data point.…”

“…Ocular fluids and tissues homogenized with iso tonic phosphate buffer (pH 7.4) were obtained in a manner similar to that described previously [8], The extent of binding of prednisolone to proteins in these fluids and tissue homogenates (10, 20, or 40%) was determined by the equilibrium dialysis technique us ing two-chambered acrylic dialysis cells. Two plates were joined tightly, with a cellulose membrane (Vis King, Ethyl Corp.) between them.…”

Vitreal Kinetics of Quinidine in Rabbits in the Presence of Topically Coadministered P-Glycoprotein Substrates/Modulators

“…PHS, a hemisuccinate ester prodrug of prednisolone (Augustijns et al, 1998), requires hydrolysis (chemical or enzymatic) of the ester bond to generate free prednisolone. The presence of esterase activity in rabbit ocular tissues has been demonstrated and well documented with ester prodrugs of pilocarpine, dipivefrin, ganciclovir, and acyclovir (Tsuji et al, 1987;Majumdar et al, 2006Majumdar et al, , 2009. Bioreversion of PHS was studied in vitreous humor and in the ocular tissues such as the cornea, iris-ciliary body, and RPE/choroid tissue as described previously (Majumdar et al, 2009).…”