Acetyl-carnosine
Encyclopedia
N-Acetylcarnosine is a naturally occurring compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 chemically related to the dipeptide carnosine
Carnosine
Carnosine is a dipeptide of the amino acids beta-alanine and histidine. It is highly concentrated in muscle and brain tissues....

. Its molecular structure is similar to carnosine with the exception that it carries an additional acetyl
Acetyl
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...

 group. This makes NAC a more stable molecule which is not easily destroyed by carnosinase, an enzyme that breaks down carnosine to its constituent amino acids, beta-alanine
Beta-alanine
β-Alanine is a naturally occurring beta amino acid, which are amino acids in which the amino group is at the β-position from the carboxylate group . The IUPAC name for β-alanine would be 3-aminopropanoic acid...

 and histidine
Histidine
Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...

.

Actions

NAC is a free-radical scavenger and is particularly active against lipid peroxidation
Lipid peroxidation
Lipid peroxidation refers to the oxidative degradation of lipids. It is the process in which free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage. This process proceeds by a free radical chain reaction mechanism...

 in the different parts of the lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...

 in the eye. It is the active ingredient of eye drops used in order to prevent or treat cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...

.

Research

During early experiments performed at the Moscow Helmholtz Research Institute for Eye Diseases, it was shown that NAC (1% concentration), was able to pass from the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

 to the aqueous humour
Aqueous humour
The aqueous humour is a clear, gelatinous fluid similar to plasma, but containing low-protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens. It is located in the space between the lens and the cornea...

 after about 15 to 30 minutes.

It is believed that NAC is deacetylated (loses its acetyl group) and transforms into carnosine, which then acts as an antioxidant and against glycation
Glycation
Glycation is the result of the bonding of a protein or lipid molecule with a sugar molecule, such as fructose or glucose, without the controlling action of an enzyme. All blood sugars are reducing molecules. Glycation may occur either inside the body or outside the body...

. In another study NAC was reported as effective in improving vision in cataract patients and reduced the appearance of cataract. The authors called this ‘a snow melting effect’ referring to the slow reduction of the cataractous tissues in the lens following the use of NAC eye drops. Transparency of the lens improved after using NAC eye drops at a concentration of 1% twice a day for four months. These results were relevant to all forms of cataract, mild or severe, although other studies found the most beneficial effect was in relation to early forms of cataract. This was a landmark study which caused many commercial operators to manufacture their own brands of anti-cataract NAC eye drops.

Chinese scientists have confirmed that the antioxidant and antiglycating effects of the carnosine molecule can be the reason why it is effective in delaying cataract development. A recent double-blind, placebo control study confirmed these early findings.

Statement by the Royal College of Ophthalmologists

The RCO issued the following public statement about N-acetyl carnosine as of August, 2008:

“The evidence for the effectiveness of N-acetyl carnosine eye drops is based on experience on a small number of cases carried out by a Russian researcher team. To date, the research has not been corroborated and the results replicated by others. The long-term effect is unknown. Unfortunately, the evidence to date does not support the 'promising potential' of this drug in cataract reversal. More robust data from well conducted clinical trials on adequate sample sizes will be required to support these claims of efficacy. Furthermore, we do not feel the evidence base for the safety is in any way sufficient to recommend its use in the short term. More research is needed”.

Since the publication of this statement, the results of new scientific trials have been made available to the Scientific Committee of the RCO.[citation needed]
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