Opposite impact of inflammation and oxidative stress on vascular GGT activity

Purpose. Gamma-glutamyltransferase (GGT) is a cell surface enzyme from the Meister cycle that catalyzes the first step in the catabolism of glutathione (GSH) and its derivative S-nitroso-glutathione (GSNO), thus allowing for both the recovery of precursor aminoacids and – with regard to GSNO – the release of nitric oxide (NO). Recent studies indicate that increased levels of GGT activity in the serum are correlated with increased cardiovascular morbidity/mortality, including atherosclerosis or hypertension, two contexts of vascular wall inflammation and oxidative stress [1]. However lesser is known on GGT activity inside the vascular wall. Our aim was to evaluate GGT activity in cells and tissue from the vascular wall in several models of inflammation and oxidative stress. Methods. GGT activity (quantified using L-γ-glutamyl-p-nitroanilide) and intracellular GSH concentrations (measured by 2,3-naphtalene dicarboxaldeide) were measured in (i) smooth muscle cells isolated from rat aortic wall (A10 line) stimulated either with LPS (20 µg/ml, 24 h 37°C) or 2,2'-azobios(2-amidinopropane) dihydrochloride (AAPH; 50mM, 2 h 37°C) to mimic inflammation or oxidative stress respectively, and (ii) in aorta homogenates from male Spontaneously Hypertensive Rats (SHR) compared to their counterparts WKY normotensive Wistar Kyoto rats. In human atherosclerotic carotid plaques, GGT expression was assessed by SDS-PAGE analysis in homogenates, using macrophages infiltration as marker of inflammation. Results. In human atherosclerotic plaques homogenates, the presence of a high-molecular weight GGT similar to that expressed by monocytes/macrophage was observed, with the highest GGT expression in presence of high vs. low macrophage infiltration (score 2: 5-10%, 3: >10% vs. 1: <0.5%). GGT activity increased in the cultured cell model of inflammation (Table 1), while it decreased in the cell and tissue models of oxidative stress in parallel with the decrease in GSH content. Conclusion. We planned to further evaluate the possible modulation between activated macrophages and promotion of pro-atherogenic process in SMC. Future experiments may also help to fully elucidate the mechanisms of GGT release and/or activity and its role during inflammation and/or oxidative stress. Keywords: Gamma-glutamyltransferase, inflammation, oxidative stress, atherosclerosis, smooth muscle cells Bibliography: 1. Pompella A, Emdin M, Passino C, Paolicchi A. The significance of serum gamma-glutamyltransferase in cardiovascular diseases. Clin. Chem. Lab. Med., 2004, 42: 1085-91.