Calcium Channel Blockade Inhibits Platelet Activating Factor Production by Human Umbilical Vein Endothelial Cells

Abstract

An increase in intracellular calcium level is an important signal in the regulation of cellular responses under normal and pathological conditions. Because two key enzymes in the synthetic pathway of platelet activating factor (PAF), phosphollpase A 2 and acetyltransferase, are calcium dependent, we hypothesized that calcium channel blockade may inhibit agonist-induced PAF synthesis. Primary cultures of human umbilical vein endothelial cells (EC), pre-incubated with [3H]acetate, were exposed to thrombin (5 U/mL) and PAF production was quantitated by incorporation of radiolabel into the EC lipid fraction co-migrating with exogenous PAF in thin-layer chromatography. The effect of pre-incubation with calcium channel blockers (verapamil, diltiazem, 10-4 M) or buffer was determined. Results (triplicate experiments, * P<0.05 vs buffer, t P<0.05 vs thrombin) demonstate that pre-incubation with calcium channel blocker markedly inhibits thrombin-induced PAF production (verapamil:buffer 273 +_ 122, thrombin 10,735 ___ 1524", thrombin + verap-mll 178 +_ 91 t cpm/plate; diltiazem:buffer 1097 +__ 581, thrombin 15,283 +__ 2661", thrombin + dlltiazem 280 ___ 56 ~ cpm/plate). The effect of diltiazem was dosedependent (% inhibition: 10 -7 M, 46%; 10-5 M, 60%; 10 -4 M, 98%). Diltiazem also inhibited bradykinin (10-s M) induced PAF synthesis. In calcium-free medium or in the presence of LaCI 3 (10 -3 M}, the PAF response of EC to thrombin was blunted (buffer 582 ___ 360, thrombin 5394 + 1069, thrombin Jr calcium free medium 1055 ___ 571, thrombin -b LaC13 1271 ----. 58 cpm/plate). We conclude that calcium channel blockers prevent agonistinduced PAF synthesis, possibly by preventing cellulax calcium influx and activation of PAF synthetic enzymes. We speculate that this mechanism may underlie, at least in part, the beneficial effect of calcium channel blockade under various pathological conditions.

Platelet activating factor (PAF) and activity of its biosynthetic and catabolic enzymes in blood and leukocytes of male patients with newly diagnosed heart failure

“…Indeed, drugs used for routine heart failure therapy such as aldosterone antagonists, angiotensin-converting enzyme inhibitors, antiarrythmic agents, statins and diuretics may modulate inflammatory response [30,31] although there are some studies not showing such effects [32]. Noteworthy examples of interactions between PAF and cardiovascular drugs include nitrates, which reduce PAF production in endothelial cells stimulated with thrombin [33], calcium channel blockers, which reduce PAF production in human umbilical vein endothelial cells [34] and salicylates, which inhibit the biosynthetic enzyme lyso-PAF AT [35].…”

Baseline and 6-Week Follow-Up Levels of PAF and Activity of Its Metabolic Enzymes in Patients With Heart Failure and Healthy Volunteers—A Pilot Study

“…40 Lyso-PAF-AT is unaffected by statins in healthy volunteers, while it seems to be strongly downregulated in patients with HF in the present study. Other possible interactions between PAF and cardiovascular drugs include nitrates and calcium channel blockers, which reduce PAF production in endothelial cells, 41 and human umbilical vein endothelial cells 42 and human umbilical vein endothelial cells, angiotensin-converting enzyme inhibitors which partly inhibit PAF effects and may lead to reduced PAF synthesis 43,44 and salicylates, which inhibit the lyso-PAF-AT. 45 From a different perspective, the trend for increase in PAF observed at the follow-up period in patients with HF may favor compensatory mechanisms of the disease.…”