Ma Hang, Liu Weixi, Frost Leslie, Kirschenbaum Louis J, Dain Joel A, Seeram Navindra P
Bioactive Botanical Research Laboratory, Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI 02881, USA.
Food Funct. 2016 May 18;7(5):2213-22. doi: 10.1039/c6fo00169f. Epub 2016 Apr 22.
Glucitol-core containing gallotannins (GCGs) are polyphenols containing galloyl groups attached to a 1,5-anhydro-d-glucitol core, which is uncommon among naturally occurring plant gallotannins. GCGs have only been isolated from maple (Acer) species, including the red maple (Acer rubrum), a medicinal plant which along with the sugar maple (Acer saccharum), are the major sources of the natural sweetener, maple syrup. GCGs are reported to show antioxidant, α-glucosidase inhibitory, and antidiabetic effects, but their antiglycating potential is unknown. Herein, the inhibitory effects of five GCGs (containing 1-4 galloyls) on the formation of advanced glycation end-products (AGEs) were evaluated by MALDI-TOF mass spectroscopy, and BSA-fructose, and G.K. peptide-ribose assays. The GCGs showed superior activities compared to the synthetic antiglycating agent, aminoguanidine (IC50 15.8-151.3 vs. >300 μM) at the early, middle, and late stages of glycation. Circular dichroism data revealed that the GCGs were able to protect the secondary structure of BSA protein from glycation. The GCGs did not inhibit AGE formation by the trapping of reactive carbonyl species, namely, methylglyoxal, but showed free radical scavenging activities in the DPPH assay. The free radical quenching properties of the GCGs were further confirmed by electron paramagnetic resonance spectroscopy using ginnalin A (contains 2 galloyls) as a representative GCG. In addition, this GCG chelated ferrous iron, an oxidative catalyst of AGE formation, supported a potential antioxidant mechanism of antiglycating activity for these polyphenols. Therefore, GCGs should be further investigated for their antidiabetic potential given their antioxidant, α-glucosidase inhibitory, and antiglycating properties.
含有葡糖醇核心的没食子单宁（GCGs）是一类多酚，其没食子酰基连接在1,5-脱水-D-葡糖醇核心上，这在天然存在的植物没食子单宁中并不常见。GCGs仅从枫属（Acer）植物中分离得到，包括药用植物红枫（Acer rubrum），它与糖枫（Acer saccharum）一起是天然甜味剂枫糖浆的主要来源。据报道，GCGs具有抗氧化、α-葡萄糖苷酶抑制和抗糖尿病作用，但其抗糖基化潜力尚不清楚。在此，通过基质辅助激光解吸电离飞行时间质谱、牛血清白蛋白-果糖和G.K.肽-核糖测定法，评估了五种GCGs（含1-4个没食子酰基）对晚期糖基化终产物（AGEs）形成的抑制作用。在糖基化的早期、中期和晚期，GCGs表现出优于合成抗糖基化剂氨基胍的活性（IC50分别为15.8-151.3 μM和>300 μM）。圆二色性数据表明，GCGs能够保护牛血清白蛋白的二级结构免受糖基化影响。GCGs不会通过捕获活性羰基物质（即甲基乙二醛）来抑制AGE形成，但在DPPH测定中表现出自由基清除活性。以ginalin A（含2个没食子酰基）作为代表性GCG，通过电子顺磁共振光谱进一步证实了GCGs的自由基淬灭特性。此外，这种GCG螯合了亚铁离子（AGE形成的氧化催化剂），支持了这些多酚抗糖基化活性的潜在抗氧化机制。因此，鉴于GCGs具有抗氧化、α-葡萄糖苷酶抑制和抗糖基化特性，应进一步研究其抗糖尿病潜力。
