Human Polymorphonuclear Leukocytes by Retinoic Acid and Inhibition of Phorbol Ester-stimulated Chemiluminescence in

Chemiluminescence (CL) is an index of both the generation of and reactions mediated by Cv and 'O2. The tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), is a potent stim ulator of CL by human polymorphonuclear leukocytes; treat ment 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 Cv 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 UM retinole acid show only a marginal CL response to TPA. Addition of retinole acid to resting polymorphonuclear leuko cytes results in a transient burst of CL without concomitant Cv 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, an 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 can exert enhanced antipromoter activities. Polymorphonu clear leukocytes provide a useful system for exploring the roles of reactive oxygen species in the mechanism of action of both TPA and retinoic acid.