| Reactive aldehydes from lipid peroxidation such as malonaldehyde (MDA), 4-hydroxynonenal (HNE) are responsible for the modification of different biological macromolecular structures and functions by reacting with either SH-groups or amino groups of bio-molecules to form seminercaptals or Schiff bases and lead to various aging-related alterations. MDA (20mM) reduced sharply the typical fluorescence of proteins (excitation 280nm/emission 350nm) and produced age pigment-like fluorescence with a strong emission peak at 460 nm excited at 395 nm when incubated at 37℃. On the other hand, malondialdehyde (MDA) in different concentrations significantly increased viscosity, plastic viscosity and yield-stress of blood materials such as human plasma and erythrocyte suspensions. Other non-peroxidated aldehydes, such as formaldehyde, acetaldehyde, glyoxal, acrolein, pyruvaldehyde, salicylaldehyde, all did not change rheological property of these biological materials. The effects of MDA on rheological parameters, crosslinking reaction and their relation with age pigment-like fluorescence were studied. Malonaldehyde, a marjor product of the peroxidation of polyunsaturated lipids, may play an essential role in the formation of the fluorescent products in lipofuscin-like fluorescent pigments and in the blood viscosity increase.Fluorescence and non-enzymatic browning were observed in reactions between ascorbic acid (AsA) and amino acids (AA) as well as in reactions involving AsA autoxidation and/or polymerization in the presence of trace amounts of adventitious iron. These reaction products exhibited fluorescent spectra (400nm-490nm) akin to those of extracts from liposcin-rich tissues.Considering that dehydroascorbic acid and MDA are active in biological system, the oxidation-enhanced carbonyl-protein cross-linking is suggested to be an important chemical reaction which may take place during ageing and be involved in lipofuscinogenesis.
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