Effects of dietary retinyl palmitate and selenium on tumoricidal capacity of macrophages in mice undergoing tumor promotion

Dietary retinyl palmitate was administered for 22-30 weeks in CD-1 mice which had been initiated with 0.15 μmol of 7,12-dimethylbenz[a]-anthracene (DMBA) and promoted with 8 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA) twice weekly thereafter. This treatment resulted in a dose response in both the tumoricidal capacity of a selected number of isolated peritoneal macrophages (PM) and in skin tumor prevention. At 350 I.U./g of diet, retinyl palmitate (RP) also resulted in a 3-fold increase in the number of DM. RP significantly increased the total capacity of macrophage host defenses by increasing the number and individual capacity for cytotoxicity. Selenium (Se), at 2 parts/million in the drinking water, did not enhance PM tumoricidal capacity, although it did result in 60% reduction of mouse tumor burden.