Glucocorticoids potently block tumour necrosis factor-alpha- and lipopolysaccharide-induced apoptotic cell death in bovine glomerular endothelial cells upstream of caspase 3 activation

1 Endothelial cell damage in glomeruli and kidney arterioles appears to pla y a pivotal role in glomerular inflammatory diseases. Glomerular endothelia l cells, a specialized microvascular cell type involved in the regulation o f glomerular ultrafiltration, die by apoptosis in response to tumour necros is factor-alpha (TNF-alpha), TNF-alpha/basic fibroblast growth factor (bFGF ), TNF-alpha/cycloheximide and bacterial lipopolysaccharide (LPS). Apoptoti c cell death is characterized by extensive DNA cleavage, DNA ladder formati on, and characteristic morphological alterations. 2 In search for apoptosis-preventing signals, we identified glucocorticoids as potent death preventing factors. Co-treatment of cells with 10 nM dexam ethasone and TNF-alpha, TNF-alpha/bFGF, TNF-alpha/cycloheximide, or LPS blo cked roughly 90% of apoptotic cell death in glomerular endothelial cells. 3 Similarly to dexamethasone (TNF-alpha- and LPS-induced apoptosis are prev ented with IC50 values of 0.8 and 0.9 nM, respectively), other synthetic an d natural forms of glucocorticoids, such as fluocinoione, prednisolone, hyd rocortisone, and corticosterone potently inhibited cell death with IC50 val ues of 0.2, 6, 50 and 1000 nM, for TNF-alpha and 0.7, 8, 100 and 500 nM for LPS, respectively. 4 Apart from glucocorticoids, mineralocorticoids such as aldosterone also b locked TNF-alpha/LPS-induced apoptosis (IC50 similar to 500 nM for TNF-alph a and similar to 500 nM for LPS), whereas sex hormones, i.e. beta-estradiol and testosterone remained without effect. 5 The protective effect of glucocorticoids (and mineralocorticoids) require d glucocorticoid receptor binding as it could be antagonized by the glucoco rticoid receptor antagonist RU-486. Concerning TNF-alpha and LPS signal tra nsduction, we found that dexamethasone efficiently prevented TNF-alpha- and LPS-induced activation of caspase-3-like proteases. Therefore, we postulat e inhibitory mechanisms upstream of terminal death pathways.