ABSTRACT
There are several experimental indications that cataract formation is induced and/or enhanced by activated oxygen species including hydrogen peroxide, superoxide radical anion, singlet oxygen and hydroxyl radical. These species can be generated chemically, enzymatically or photodynamically. Taking advantage of endogenous photodynamic compounds in isolated lens, aqueous humor or vitreous preparations in the presence of S-methyl-alpha-ketobutyric acid (KMB), ethylene formation can be monitored for at least 2 h of light-dependent KMB degradation. This reaction is extremely sensitive and can be inhibited by potassium iodide in low concentrations. This model reaction might be useful for studying possibly inhibiting substances or stimulating processes involved in cataract formation.
Subject(s)
Aqueous Humor/metabolism , Ethylenes/biosynthesis , Lens, Crystalline/metabolism , Light , Methionine/analogs & derivatives , Animals , Cataract/etiology , Cattle , Methionine/metabolism , Potassium Iodide/pharmacology , Vitreous Body/metabolismABSTRACT
The aqueous humor and lenses of rabbit eyes contain inhibitors of photodynamic destructions. Preparations of vitreous, however, more likely seem to contain stimulatory compounds. The anticataractic drug Pherajod significantly blocks the photodynamic formation of destructive oxygen species. Inhibition by 65% of photodynamic destructions, measured as ethylene release from S-methyl-a-ketobutyric acid in the riboflavin-driven oxygen photoactivation, is observed with aqueous humor preparations isolated 5 min after start of incubation of rabbit eyes in Pherajod solution.
Subject(s)
Eye/metabolism , Potassium Iodide/metabolism , Animals , Aqueous Humor/metabolism , Kinetics , Lens, Crystalline/metabolism , Rabbits , Vitreous Body/metabolismABSTRACT
Potassium iodide (KI) passes the cornea of isolated rabbit eyes with kinetics of approximately 0.25 mumol/h/ml aqueous humor. In photodynamic reactions, simulated as light-dependent decay of S-methyl-alpha-ketobutyric acid in the presence of riboflavin, KI acts as an antioxidant cooperating with internal scavengers such as ascorbate. With the simple model reactions applied it may be possible to study mechanism and functions in vivo of eye-protecting factors or combinations of compounds.
