Significance Of Carbonyl-Amino Reaction In Age Pigment Formation

Senescence is a collective consequence of both inheritance and environment. The aging hypothesis of carbonyl stress suggests that reactive unsaturated aldehydes and ketones produced in lipid peroxidation and glycation can inevitably result in carbonyl-amino reaction with macromolecules in body, it is the essence of aging process. This paper discussed the free radical theory of aging, the glycation theory of aging and directed to the carbonyl stress theory of aging, which was implied from the biochemistry of age pigment formation. Based the relationship between carbonyl stress and neurodegenerative diseases, histamine (HA) — an important neurotransmitter and inflammatory factor in the pathological situations — was investigated to react with one of the secondary products in lipid peroxidation—malondialdehyde (MDA). The influance of the reaction between ascorbic acid (AsA) and glutamine (Gln) on age pigments formation was also investigated in this study.The studies included in the thesis are summarized as follows: 1. Studying the reaction between HA and MDA to explore the mechanism of carbonyl stress-related toxification on neurotransmitter HA and the potential de-carbonylation function of HA. The mixture of MDA and HA at pH7.4, 37℃ was assayed by high performance liquid chromatography (HPLC), spectrophotometry and spectrofluorometry. The reaction products were assayed by LC/MS. Inphysioligical condition, the reaction of MDA and HA yielded two products: a nonfluorescent enaminal derivatives and a fluorescent 1, 4-dihydropyridine adducts. The fluorescence maxima of the fluorescent products (Ex. 393nm / Em. 464nm) were similar to those of lipofuscin pigment. The fluorescence intensity of reaction mixture was in direct proportion to the MDA concentration. This study suggested that the reaction of HA with MDA may reveal toxic effect of unsaturated carbonyls in the brain and may reflect a novel de-carbonylation function of histamine under various pathological conditions.2. Influence of the reaction between ascorbic acid (AsA) and glutamine (Gin) on age pigments formation was studied. AsA, after being oxidized in physiological condition (pH7.4, 37°C), reacted with Gin to form the stable fluorophores showing lipofuscin-like fluorescence (Ex350/Em430). The fluorescence intensity reached a plateau level after increase and was found in direct proportion to the AsA and Gin concentations. The mechanism of the production of cross linking fluorophores may be furaldehyde which was produced by oxidized AsA polymerizing with Gin. The essence of this reaction is carbonyl-amino reaction. Considering that AsA and dehydro-AsA are active and common reductones, the cross linking process resulting in fluorophores by the AsA/Gln reaction is suggested to be an importantchemical reaction which may take place during lipofuscin formation and aging.