Mercury Activates Phospholipase A₂ and Induces Formation of Arachidonic Acid Metabolites in Vascular Endothelial Cells

ABSTRACT

Currently, mercury has been identified as a risk factor in cardiovascular diseases among humans. Here, we tested our hypothesis that mercury modulates the activity of the vascular endothelial cell (EC) lipid signaling enzyme phospholipase A₂ (PLA₂), which is an important player in the EC barrier functions. Monolayers of bovine pulmonary artery ECs (BPAECs) in culture, following labeling of membrane phospholipids with [³H]arachidonic acid (AA), were exposed to the inorganic form of mercury, mercury chloride, and the release of free AA (index of PLA₂ activity) and formation of AA metabolites were determined by liquid scintillation counting and enzyme immunoassay, respectively. Mercury chloride significantly activated PLA₂ in BPAECs in a dose-dependent (0 to 50 μM) and time-dependent (0 to 120 min) fashion. Metal chelators significantly attenuated mercury-induced PLA₂ activation, suggesting that cellular mercury–ligand interaction is required for the enzyme activation and that chelators are suitable blockers for mercury-induced PLA₂ activation in ECs. Sulfhydryl (thiol-protective) agents, calcium chelating agents, and cPLA₂-specific inhibitor also significantly attenuated the mercury-induced PLA₂, suggesting the role of thiol and calcium in the activation of cPLA₂ in BPAECs. Significant formation of AA metabolites, including the release of total prostaglandins, thromboxane B₂, and 8-isoprostane, were observed in BPAECs following their exposure to mercury chloride. Mercury chloride induced cytotoxicity as observed by the altered cell morphology and enhanced trypan blue uptake, which was attenuated by the cPLA₂ inhibitor AACOCF₃. The results of this study revealed that inorganic mercury-induced PLA₂ activation through the thiol and calcium signaling and the formation of bioactive AA metabolites further demonstrated the association of PLA₂ with the cytotoxicity of mercury in ECs. Overall, the results of the current study underscore the importance of PLA₂ signaling in mercury-induced endothelial dysfunctions.

KEYWORDS :

• Arachidonic Acid
• Isoprostane
• Lipid Signaling
• Mercury
• Phospholipase A₂
• PLA₂
• Prostaglandin
• Thromboxane B₂
• Vascular Endothelial Cells