The Natural Histidine-Containing Dipeptide N^alpha-Acetylcarnosine as an Antioxidant for Ophthalmic Use

M. A. Babizhayev^1,2*, V. N. Yermakova², Yu. A. Semiletov¹, and A. I. Deyev¹

¹Innovative Vision Products, Inc., 3511 Silverside Road, Suite 105, County of New Castle, Delaware, USA 19810

²Moscow Helmholtz Research Institute of Eye Diseases, ul. Sadovaya-Chernogryazskaya 14/19, Moscow, 103064 Russia; fax: (7-095) 977-2387; E-mail: markbabizhayev@mail.ru

^* To whom correspondence should be addressed.

Received January 25, 1999; Revision received February 7, 2000

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The naturally occurring compound N^alpha-acetylcarnosine is proposed as a prodrug of L-carnosine that is resistant to enzymatic hydrolysis by carnosinase. Eyes of rabbits were treated with 1% N^alpha-acetylcarnosine, L-carnosine, 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) and thin-layer (TLC) and ion-exchange chromatographic techniques. Topical administration of pure L-carnosine 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. N^alpha-Acetylcarnosine showed dose-dependent hydrolysis in its passage from the cornea to the aqueous humor, releasing L-carnosine after l5-30 min of ocular administration of the prodrug in a series of therapeutic modalities: instillation <= subconjunctival injection <= ultrasound-induced phoresis. Different treatment techniques showed excellent toleration of 1%N^alpha-acetylcarnosine by the eye. Once in the aqueous humor, L-carnosine might act as an antioxidant and enter the lens tissue when present at effective concentrations (5-l5 mM). The advantage of the ophthalmic prodrug N^alpha-acetylcarnosine and its bioactivated principle L-carnosine as universal antioxidants relates to their ability to give efficient protection against oxidative stress both in the lipid phase of biological membranes and in aqueous environments. N^alpha-Acetylcarnosine is proposed for treatment of ocular disorders that have a component of oxidative stress in their genesis (cataracts, glaucoma, retinal degeneration, corneal disorders, ocular inflammation, complications of diabetes mellitus, and systemic diseases).

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KEY WORDS: antioxidant, natural dipeptide, N^alpha-acetylcarnosine, prodrug, L-carnosine, aqueous humor, lens, cataract, ocular administration

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