Advanced glycation end-products
Proteins, nitrogen free radicals and reducing sugars are part of what is known as the Maillard reaction, a mechanism first described by Hodge in 1953 which produces fused glycated crosslinks in tissue . These crosslinks are also commonly known as advanced glycation end-products (AGEs) and are the final result of a complex series of chemical reactions.
AGEs form an intra and intermolecular web-like structure between adjacent proteins, impairing their function and altering their physical properties [2-3]. The accumulation of crosslinks is thought to be one of the reasons why we age and they can be a factor in aging and in the development or worsening of many degenerative diseases, such as diabetes, atherosclerosis, chronic kidney disease, and Alzheimer’s disease [4-5].
In healthy people the accumulation of AGEs increases slowly with age  but in diabetic patients the rate of AGE accumulation and crosslinking is significantly faster due to higher levels of glucose in the bloodstream .
There are a number of therapeutic approaches including the prevention of AGE formation via control of blood sugar in diabetics, the inhibition of AGE and even AGE breakers that are able to destroy the crosslinks. There are a number of molecules known to be able to inhibit the formation of AGEs are various stages of its formation . Inhibition tends to slow down the accumulation of glycated proteins with a fast or medium turnover but so far nothing appears effective against slow turnover proteins such as collagen in the skin or elastin in the blood vessel walls. The discovery of molecules capable of breaking down slow turnover protein crosslinks would be a major step in treating age-related diseases like diabetes and hypertension as well as the aging process itself.
The problem is there are many different types of AGEs all based on different molecules such as pentosidine, methylglyoxal lysine dimer and glucosepane. Glucosepane is the most numerous AGE found in people and therefore it is the crosslink of most interest to researchers [9-10]. Because crosslinks have a diverse range of sources there is highly unlikely to be a single breaker able to destroy all crosslinks so the race is on to find breakers for the most problematic AGEs such as glucosepane.
Alagebrium or ALT-711 was a reported back in 1996 as being able to break crosslinks, however the type of crosslink that it was alleged to break was not described . It was later discovered in 2013 that it was able to break alpha-dicarbonyl groups present in Amadori products before the formation of crosslinks .
The natural world has been mined for potential AGE breakers and in 2015 a research study investigated the potential of rosmarinic acid as an crosslink breaker and compared it to a number of other compounds. The inter-molecular crosslinking of proteins causes protein polymerization and the level of polymerization after the reaction of proteins with reducing sugar is an excellent biomarker for AGE crosslinks .
The researchers in this study set out to create an in vitro method of evaluating the rate of AGE crosslinking in albumin and to see if rosmarinic acid was able to break AGE crosslinks.
The results of the study speak for themselves and we can see that rosmarinic acid was more effective at breaking alpha-dicarbonyl AGEs than alagebrium. Not only did it reduce alpha-dicarbonyl AGE radicals but was able to break down preformed AGE-related albumin crosslinks too. This shows that rosmarinic acid extracted from rosemary produces similar results to alagebrium, and that a naturally occurring molecule extracted from herbs is able to break at least two types of protein crosslinks in vitro.
|Compound||Crosslinks breaking ability|
A further study builds on these results
A further 2016 research study builds on these results . This study investigated the effect of the two main components of rosemary extracts, namely rosmarinic acid and carnosic acid, on the formation of advanced glycation end-products in vitro.
The above chart shows that rosmarinic acid was able to inhibit the formation of AGEs by 97.4% at a dosage of 400 lg/ml. Carnosic acid had stronger inhibition at lower dosages, however when reaching concentrations over 100 lg/mg that rate of inhibition dropped off and was less significant as the dose increased. Rosmarinic acid on the other hand continued to increase inhibition in a dose-dependent manner with higher doses leading to increasing inhibition.
This study provides evidence that the both rosmarinic acid and carnosic acid both inhibit the formation of AGEs (both fluorescent and nonfluorescent types) in vitro. Both compounds decreased the rate of AGE formation by the following mechanisms:
The reducing of the contents of dicarbonyl compounds such as glyoxal and methylglyoxal by carnosic acid and methylglyoxal by rosmarinic acid.
Decreasing protein carbonylation.
Inhibiting the formation of the adduct between carbonyl compounds and proteins.
Rosmarinic acid has a long and well documented history of being safe and could be a useful supplement to combat certain types of AGE crosslinks. It has implications for the treatment of diabetes, skin aging, neuropathy and retinopathy. Whilst the AGEs rosmarinic acid reduces and breaks down are not the only AGEs that accumulate during the aging processes removing them could prove useful in maintaining health.
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