Epigallocatechin gallate affects glucose metabolism and increases fitness and lifespan in Drosophila melanogaster

Abstract

In this study, we tested whether a standardized epigallocatechin-3-gallate (EGCG) rich green tea extract (comprising > 90% EGCG) affects fitness and lifespan as well as parameters of glucose metabolism and energy homeostasis in the fruit fly, Drosophila melanogaster. Following the application of the green tea extract a significant increase in the mean lifespan (+ 3.3 days) and the 50% survival (+ 4.3 days) as well as improved fitness was detected. These effects went along an increased expression of Spargel, the homolog of mammalian PGC1α, which has been reported to affect lifespan in flies. Intriguingly, in flies, treatment with the green tea extract decreased glucose concentrations, which were accompanied by an inhibition of α-amylase and α-glucosidase activity. Computational docking analysis proved the potential of EGCG to dock into the substrate binding pocket of α-amylase and to a greater extent into α-glucosidase. Furthermore, we demonstrate that EGCG downregulates insulin-like peptide 5 and phosphoenolpyruvate carboxykinase, major regulators of glucose metabolism, as well as the Drosophila homolog of leptin, unpaired 2. We propose that a decrease in glucose metabolism in connection with an upregulated expression of Spargel contribute to the better fitness and the extended lifespan in EGCG-treated flies.

Keywords: Drosophila melanogaster; Gerotarget; epigallocathechin-3-gallate; green tea; life span.

Figure 1. Effect of EGCG (10 mg/ml) supplementation on lifespan in male W¹¹¹⁸ Drosophila melanogaster

a. One representative experiment out of two is shown. n = 120 flies per group, p < 0.05 log-rank test. b. Relative fitness levels of male W¹¹¹⁸ Drosophila melanogaster reared on an EGCG (10 mg/ml)-supplemented diet for 30 days. The data are expressed as the mean + SEM (n = 100). * indicates significant differences compared to the control group (p < 0.05, Student's t-test).

Figure 2. EGCG-dependent inhibition of α-amylase and α-glucosidase activity in vitro (a, b) and in vivo (c, d) and decrease of glucose levels in vivo (e)

Dose-dependent inhibition of a. α-amylase and b. α-glucosidase by EGCG in vitro. The data are expressed as the mean + SEM (n = 3). c. α-amylase activity, d. α-glucosidase activity, and e. glucose levels of male W¹¹¹⁸ Drosophila melanogaster relative to fly weights. Flies were reared on an EGCG (10 mg/ml)-supplemented or control diet for 10 days. The data are expressed as the mean + SEM (n = 5–6, indicating extraction from 5–6 × 5 flies). * indicates significant differences in EGCG-treated flies compared to flies fed control medium for 10 days (p < 0.05, Student's t-test).

Figure 3. Predicted binding modes of EGCG docked with the X-ray structure of human salivary α-amylase and with the homology model of α-glucosidase from baker's yeast

a. The interaction between EGCG and human salivary α-amylase. Illustration of the surface of the substrate binding cleft with bound EGCG (green sticks) and the 3D-superposed acarbose (yellow sticks) from pancreatic α-amylase to visualize pseudo-substrate position (yellow) within the ligand binding cleft relative to docked EGCG inhibitor (green). b. The interaction between EGCG and α-glucosidase from baker's yeast. Illustration of the surface of the substrate binding cavity bound to its competitive inhibitor maltose (grey sticks) relative to docked EGCG (green sticks). Images were depicted using the Pymol software.

Figure 4. Protein (a) and mRNA (b-e) levels of genes involved in energy homeostasis in Drosophila melanogaster

a. p-AMPK protein levels analyzed in whole fly homogenates following a 10 day treatment of male W¹¹¹⁸ Drosophila melanogaster with 10 mg/ml EGCG. b. spargel (srl), c. unpaired 2 (upd2), d. phosphoenolpyruvate carboxykinase (Pepck), and e. insulin-like peptide 5 (Ilp5) mRNA levels of genes involved in energy homeostasis measured in whole fly homogenates after a 10 day supplementation period of male W¹¹¹⁸ Drosophila melanogaster with 10 mg/ml EGCG. The data are expressed as the mean + SEM (n = 3, indicating extraction from 3 × 5 flies). * indicates significant differences in EGCG-treated flies compared to flies fed control medium for 10 days (p < 0.05, Student's t-test).

Figure 5

Schematic summary of the postulated mechanism how EGCG mediates lifespan extension and improved fitness in Drosophila melanogaster (for detailed description see text).