Effect of α-Glucosylation on the Stability, Antioxidant Properties, Toxicity, and Neuroprotective Activity of (-)-Epigallocatechin Gallate.

(-)-Epigallocatechin gallate (EGCG), the predominant catechin (>= 50%) in green tea (Camellia sinensis), displays several bioactive properties but its stability and bioavailability are low. In this work, the properties of two alpha-glucosyl derivatives of EGCG (3'-and 7-O-alpha-D-glucopyranoside), obtained by enzymatic synthesis, were assessed. The alpha-glucosylation enhanced the pH and thermal stability of EGCG. The analysis of scavenging activity toward ABTS(center dot) + radicals showed that the alpha-glucosylation at C-7 of A-ring caused a higher loss of antioxidant activity compared with the sugar conjugation at C-3' of B-ring. The 3'-glucoside also showed higher potential to alleviate intracellular reactive oxygen species (ROS) levels and to boost REDOX activity. The toxicity of EGCG and its monoglucosides was tested in human SH-S5Y5 neurons, RAW 264.7 macrophages, MRC5 fibroblasts, and HT-29 colon cancer cells. Interestingly, the 3'-O-alpha-D-glucoside increased the viability of neural cells in vitro (2.75-fold at 100 mu M) in the presence of H2O2, whilst EGCG gave rise only to a 1.7-fold enhancement. In conclusion, the alpha-glucoside of EGCG at C-3' has a great potential for nutraceutical, cosmetic and biomedical applications.