CYCLOSPORINE-A INHIBITS LEUKOTRIENE PRODUCTION IN INTACT RBL-1 CELLS WITHOUT INHIBITING LEUKOTRIENE BIOSYNTHETIC-ENZYMES

The effects of cyclosporin A (CSA) on arachidonic acid (AA) metabolism were investigated in intact rat basophilic leukemia-1 (RBL-1) cells a nd cell lysates, Calcium ionophore (A23187)-stimulated synthesis of cy steinyl leukotrienes (LTC(4), LTD(4), and LTE(4)), LTB(4), and 5-hydro xyeicosatetraenoic acid (5-HETE) in intact cells in the absence or pre sence of CSA was measured by reversed-phase high-performance liquid ch romatography (HPLC). CSA inhibited the production of cysteinyl LTs, LT B(4), and 5-HETE in intact cells in a dose-dependent manner. The synth esis of cysteinyl LTs, LTB(4), and 5-HETE was also measured after the incubation of cell lysates with free AA in the absence or presence of CSA. CSA did not inhibit synthesis of cysteinyl LTs, but rather stimul ated production of LTB, and 5-HETE in cell lysate, A23187-stimulated r elease of incorporated [H-3]AA from intact cells was not inhibited by CSA. CSA did not inhibit the synthesis of cysteinyl LTs and LTB(4) whe n cells incubated with LTA(4) as the substrate. These results indicate that the inhibitory effects of CSA on the synthesis of LTs and 5-HETE in intact cells are attributable to a modulatory action on a step in the series of intracellular events that includes the activation of 5-l ipoxygenase, which are initiated by Ca2(+) influx and end in the relea se of metabolites from the cell membrane, rather than to a direct inhi bitory action on enzymes in the LT biosynthetic pathway.