Tumor Necrosis Factor-Mediated Effects on Gamma-Glutamyl Transpeptidase Activity in Cloned Cerebral Endothelial Cells

Abstract

Gamma-glutamyl transpeptidase (γ-GTP), a marker enzyme for blood brain barrier (BBB) function, was induced consistently by TNF (500 U/mL) in cerebral endothelial cells (cEC) compared with control cultures. The enzyme activity was found to be considerably lower in pulmonary artery cells, where, when treated with TNF (500 U/mL), the induction was not observed. Pre-incubation with zinc (1 μg/mL)-enriched media for 48 hours did not block TNF-mediated activation of γ-GTP. The increase in γ-GTP activity does not appear to be mediated through the cAMP signal transduction pathway as evidenced by the lack of TNF-mediated intracellular accumulation of cAMP. In addition, forskolin failed to influence γ-GTP enzyme activity, which further suggests that cAMP is not involved. Phospholipase A2, an enzyme involved in the arachidonic acid pathway, appears to be implicated in TNF signalling across the membrane of cEC. Two inhibitors of phospholipase A2, mepacrine and p-bromophenacyl-bromide (BPB), depressed the activity of ...