Inhibiton of phorbol ester-stimulated chemiluminescence in human polymorphonuclear leukocytes by retinoic acid and 5,6-epoxyretinoic acid.

Chemiluminescence (CL) is an index of both the generation of and reactions mediated by O2-. and 1O2. The tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), is a potent stimulator of CL by human polymorphonuclear leukocytes; treatment with TPA (100 ng/ml) provokes a CL response that peaks within five min and persists for over 30 min. The response is proportional to concentration over the range of one to 100 ng/ml. The ability of different phorbol diesters to stimulate both CL and O2-. production correlates with their relative activities as tumor promoters in vivo. Non-phorbol diester tumor promoters such as iodoacetic acid, anthralin, and tween 60 are inactive in this system. The TPA-mediated stimulation of CL can be inhibited by retinoids; cells preincubated for 15 min with 100 microM retinoic acid show only a marginal CL response to TPA. Addition of retinoic acid to resting polymorphonuclear leukocytes results in a transient burst of CL without concomitant O2-. release, observations indicative of an excitable substrate. A similar CL response is seen when retinoic acid is incubated with potassium superoxide in a cell-free system. 5,6-Epoxyretinoic acid, and even more effective inhibitor of TPA-stimulated CL than retinoic acid when added simultaneously with TPA, does not undergo these two CL reactions. Thus, it appears that retinoic acid may undergo oxidative activation to a species that exert enhanced antipromoter activities. Polymorphonuclear leukocytes provide a useful system for exploring the roles of reactive oxygen species in the mechanism of action of both TPA and retinoic acid.