數種植物萃取物及 2,4,6-Trihydroxybenzoic acid 對活性雙羰基化合物之捕捉作用

Abstract

It has been demonstrated that reactive dicarbonyl species (RCS) irreversibly modified proteins over time and yielded the advanced glycation endproducts (AGEs), which are closely associated with several pathophysiological conditions, such as cataracts, diabetes complications, and Alzheimer’s disease. Methylglyoxal (MG) is one of the RCS. Higher levels of MG were observed in diabetic patients’ plasma than those in healthy people’s plasma. Thus decreasing the levels of MG will be a useful approach to prevent the formation of AGEs. The aims of the present study are to evaluate MG trapping ability of some plant extracts which were rich in phenolic compounds such as tea, bilberries, black currants, grape seeds and mulberry leaves, and one of the phenolic compounds, 2,4,6-trihydroxybenzoic acid (THBA) in simulated physiological conditions (pH 7.4 and 37 °C). The first part of current research was to evaluate the MG trapping abilities of selected plant extracts. Black, paochung and green tea leaves were extracted by boiling water, the MG trapping abilities were determined in the order of green tea, paochung tea and black tea. The result was highly correlated to their total phenolic contents. Bilberry and black currant extracts are rich in anthocyanins. When they reacted with MG at high pH conditions, both of them exhibited good MG trapping abilities. Their abilities were even better than the positive control, EGCG, when the anthocyanin equivalents were 2-3 times than MG concentration. The MG trapping ability difference between the two extracts might come from the different anthocyanin compositions of bilberry and black currant. The major compounds in grape seed extract are proanthocyanidins, the result showed that it also exhibited a good MG trapping ability. Mulberry leaves are rich in flavonoids such as quercetin, but its ability in MG trapping was not as good as those extracts rich in catechins, anthocyanins and proanthocyanidins. The second part of current research is to study the reaction between THBA and MG. THBA is a phenolic acid, which could be hydrolyzed from tannins of seaweeds or degraded from anthocyanins of tart cherries, and the structure is similar to phloretin, an antioxidant compound in apple. Our results showed that THBA is able to trap MG efficiently. The time for 50% MG reduction (t1/2) at 3 mM and 1.45 mM were determined to be 27.170 minutes and 28.367 minutes, respectively. THBA concentrations that can reduce 50% MG (EC50) were 0.835 mM THBA at 3 mM MG and 0.724 mM THBA at 1.45 mM MG.. To determine the structure of reaction adducts, THBA was react with MG in the ratio of 1:3 and 1:20 for 3 hours. The reaction mixtures were separated by HPLC, and reaction adducts collected for ESI mass spectroscopic analysis. At the ratio of 1:3, the molecular weight of adduct was shown to be 242 indicating one MG molecule was added onto one THBA molecule. At the ratio of 1:15, we got two compounds with molecular weight of 242 and 314, indicating that there were two compounds formed in the reaction, which might be one MG molecule added onto one molecule of THBA, and two MG molecules added onto one molecule of THBA.