Epigallocatechin gallate reduces vascular inflammation in db/db mice possibly through an NF-κB-mediated mechanism

Abstract

Scope: Hyperglycemia-induced vascular inflammation resulting in the adhesion of monocytes to endothelium is a key event in the pathogenesis of atherosclerosis in diabetes. We investigated whether epigallocatechin gallate (EGCG), a major catechin found in green tea, reduces vascular inflammation in diabetes.

Methods and results: Human aortic endothelial cells (HAEC) were pretreated with green tea catechins before the addition of high glucose (25 mM) for 72 h. EGCG at physiologically achievable concentration (1 μM) significantly inhibited high glucose induced adhesion of monocytes to HAEC both in static and under flow conditions. EGCG also reduced nuclear factor κB (NF-κB) regulated transcriptional activity in ECs. Six-week-old diabetic db/db mice were fed a diet containing 0% or 0.1% EGCG for 8 weeks. ECs were isolated from aortic vessels of db/db, db/db-EGCG, and control db/+ mice. EGCG supplementation greatly suppressed diabetes-increased monocytes adhesion to ECs, which is associated with reduced circulating levels of chemokines, and reduced secretions of chemokines and adhesion molecules by aortic ECs from db/db-EGCG mice. EGCG treatment reduced nuclear translocation of NF-κB p65 in aortic vessels, decreased blood pressure and serum concentrations of cholesterol and triglycerides in db/db-EGCG mice.

Conclusion: EGCG may have a direct protective effect against vascular inflammation in diabetes.

Figure 1

HAEC were pre-treated with catechins for 1 h before the addition of high glucose (25 mM) for 72 h and cell adhesion was measured using fluorescent labeled THP-1 monocytes. (A) EGCG inhibited high glucose-induced monocyte adhesion to ECs in static condition. Values are mean ± SEM, n=4 (means of quadruplicates). (B) EGCG inhibited high glucose stimulated adhesion of monocytes to ECs under shear flow control. Values are mean ± SEM, n=3 (means of 20 fields). Please also see supplemental online material for the images. (C) The effect of EGCG on high glucose-induced monocyte adhesion to ECs is structure-specific. Values are mean ± SEM, n=3 (means of quadruplicates). EC, epicatechin; ECG, epicatechin gallate; EGC, epigallocatechin; EGCG, epigallocatechin gallate; and HG, high glucose. Means without a common letter differ, P < 0.05.

Figure 2

BAEC were co-transfected with NFκB promoter-luciferase vector and pRL reporter control plasmid. 24 h after transfection, BAEC were treated with EGCG for 1 h before addition of high glucose (25 mM) for 72 h. Luciferase activity, normalized to pRL activity in the cell extracts, was determined. EGCG inhibited high glucose induced NFκB-regulated gene transcription in BAEC. Values are mean ± SEM, n=3 (means of duplicates). EGCG, epigallocatechin gallate; HG, high glucose. Means without a common letter differ, P < 0.05.

Figure 3

EGCG treatment reduced (A) adhesion of monocytes to ECs, (B) serum levels of MCP-1/JE and KC, and (C) serum levels of soluble adhesion molecules sICAM-1 and cVCAM-1in diabetic db/db mice. Values are mean ± SEM, n=6 (means of quadruplicates) for A and n=8 (means of duplicate) for B and C. Means without a common letter differ, P < 0.05.

Figure 4

Dietary EGCG reduced the secretion of (A) chemokines and (B) adhesion molecules from aortic ECs of diabetic db/db mice. Values are mean ± SEM, n=6 (means of duplicate). Means without a common letter differ, P < 0.05.

Figure 5

(A) p65 nuclear translocation increased in aorta of db/db mice and EGCG supplementation greatly suppressed this translocation in db/db mice. (B) Total NFκB p65 protein expression in arotic vessels of the mice. Values are mean ± SE, n=5 (means of duplicate). Means without a common letter differ, P < 0.05.