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The naturally occurring compound N alpha-acetylcarnosine (NAC) is proposed as the prodrug of L-carnosine (C) resistant to enzymatic hydrolysis by human serum carnosinase. Rabbit eyes were treated with 1% NAC, C or placebo and extracts of the aqueous humor from the anterior eye chamber were analyzed for imidazole content by reverse phase analytical high performance liquid chromatography (HPLC), thin-layer (TLC) and ion-exchange chromatographic techniques. The topical administration of pure C to the rabbit eye did not lead to accumulation of this compound in the aqueous humor over 30 min in concentration exceeding that in the placebo-treated matched eye. NAC showed dose-dependent hydrolysis in its passage from the cornea to the aqueous humor, releasing C after 15. 30 min of ocular administration of prodrug in a series of therapeutical modalities: instillation < or = subconjunctival injection < or = ultrasound induced phoresis. Different treatment techniques showed excellent toleration of 1% NAC by the eye. Once in the aqueous humor, C might act as an antioxidant and enter the lens tissue when present at effective concentrations (5-15 mmol/l). The advantage of the ophthalmic prodrug NAC and its bioactivated principle C as universal antioxidants relates to their ability to give efficient protection against oxidative stress both in the lipid phase of biological membranes and in an aqueous environment. NAC is proposed to treat ocular disorders which have the component of oxidative stress in their genesis (cataracts, glaucoma, retinal degeneration, corneal disorders, ocular inflammation, complications of diabetes mellitus, systemic diseases).