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The quantum dots (QDs) community has raised great concerns about the exposure and possible cytotoxicity impact of QDs to biological systems since the majority of QDs are made from heavy metals such as cadmium and lead. It is well known that macrophage cells serve as the first line of immune defense against exogenous substances, but the toxicity of QDs on macrophages remains poorly understood to date and some reported literature even have shown inconsistent results. In this study, we aimed at investigating the cytotoxicity and immune response of CdSe/ZnS QDs in mouse macrophage cells. Our confocal images showed that CdSe/ZnS QDs were captured by macrophages and were located in the cytoplasmic region. The flow cytometry assay showed that the uptake efficiency of QDs within cells was as high as 90%. More importantly, the cells treated with QDs showed a decrease in the cell viability and an enhanced gene transcription of cytokines IL-6 and TNFa was observed, but no changes were detected in the mechanism of releasing cytokines IL-6 and TNFa in the cells. These results suggest that the treatment of CdSe/ZnS QDs is indeed affecting the cell viability of the macrophages but did not cause any obvious immune response changes in the cells.

Analysis of the binding interaction of (−)-epigallocatechin-3-gallate (EGCG) and pepsin is important for understanding the inhibition of digestive enzymes by tea polyphenols. We studied the binding of EGCG to pepsin using fl uorescence spectroscopy, Fourier transform infrared spectroscopy, isothermal titration calorimetry, and protein-ligand docking. We found that EGCG could inhibit pepsin activity. According to thermodynamic parameters, a negative ΔG indicated that the interaction between EGCG and pepsin was spontaneous, and the electrostatic force accompanied by hydrophobic binding forces may play major role in the binding. Data from multi-spectroscopy and docking studies suggest that EGCG could bind pepsin with a change in the native conformation of pepsin. Our results provide further understanding of the nature of the binding interactions between catechins and digestive enzymes.Keywords: EGCG, green tea, pepsin, digestion, interactionGreen tea has many potential health benefi ts attributed to tea polyphenols, in particular catechins, which have strong antioxidative activity (SABU et al., 2010). Major te a catechins include (−)-epigallocatechin-3-gallate (EGCG), (−)-epigallocatechin, (−)-epicatechingallate and (−)-epicatechin. EGCG is the most potent constituent of green tea and represents 50% of the total catechins (KILMARTIN & HSU, 2003). Tea polyphenols are soluble in water and can be added to various foods as natural antioxidants. However, tea polyphenols may reduce food digestibility by inhibiting digestive enzymes. Studies have shown that phenolic compounds from plants have a strong ability to interact with food proteins and show strong complexing abilities with enzymes (SPENCER et al., 1988;DUBEAU et al., 2010;YUKSEL et al., 2010;BANDYOPADHYAY et al., 2012). The binding interactions of tea catechins with digestive enzymes were found to denature the catalytic activity of enzymes, which reduced food digestibility (HE et al., 2006). Pepsin is a proteinase present in animals and has a signifi cant role in the digestive process. Therefore, studying the interactions of EGCG and pepsin are important to understand its mechanism of action to inhibit pepsin.Pepsin contains 2 tryptophans (Trp) and 4 tyrosines (Tyr) therefore, fl uorescence quenching can be used with the intrinsic tryptophan of Trp and Tyr to determine the binding affi nities of EGCG and pepsin and characterise the nature of the EGCG-pepsin complex.In this study, we detected the inhibitory effect of EGCG on pepsin activity by studying the interaction of EGCG and pepsin with fl uorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and isothermal titration calorimetry (ITC). To substantiate our experimental studies, docking studies were performed. Important information, such as the change in protein secondary structure and association constant, are reported. We aimed to help understand the nature of binding between catechins and digestive enzymes.

The leaves of Ligustrum purpurascens are used in a Chinese traditional tea called small-leaved kudingcha, which is rich in phenylpropanoid glycosides (PPGs) and has many beneficial properties. Two critical exoacting glycoside hydrolase enzymes (glucosidases) involved in carbohydrate digestion are a-glucosidase and a-amylase. We investigated the properties of PPGs from L. purpurascens for inhibiting a-amylase and a-glucosidase activity in vitro and found IC 50 values of 1.02 and 0.73 mg mL À1 , respectively. The patterns of inhibiting both a-amylase and a-glucosidase were mixed-inhibition type. Multispectroscopy and molecular docking studies indicated that the interaction between PPGs and a-amylase and a-glucosidase altered the conformation of enzymes, with binding at the site close to the active site of enzymes resulting in changed enzyme activity. Our studies may help in the further health use of small-leaved kudingcha.