Propolis is a resinous material gathered by honeybees from the buds and bark of certain trees and plants. In Japan, propolis is widely used as a health food and the Japanese believe that it can cure inflammation, heart disease, and even diabetes and cancer. Biological properties of propolis have become a point of particular interest recently.1) The most used formulation in folk medicine is the ethanol extract.
2)Chemical analysis indicated that propolis is a multicomponent mixture of various compounds with prevalence of flavonoids and phenolic acids.3) Several biological attributes such as anticancer, antioxidant, antimicrobial, anti-inflammatory and antibiotic activities have been reported for propolis.4) The standardization of propolis preparations is indeed difficult because of changes in chemical composition and pharmacological activities, resulting from variation in geographical and botanical origin.5) It is important to investigate their mechanisms of action in order to predict possible therapeutic and toxic effects, and to also use this information to develop and design new drugs that are even more effective for the prevention and treatment of cancer. We are interested in the effects of various natural products on cell growth in human cancer cells, as predictors of novel agents that may be useful in cancer chemoprevention or therapy.6) In this study, the inhibitory effects of propolis, a new preparation (CB Propolis) isolated from Brazilian propolis, on the growth of the human leukemia cell line U937 and on the synthesis of DNA, RNA and protein in U937 cells are discussed.
MATERIALS AND METHODSChemicals Aqueous solution of propolis, 7) CB Propolis (the dried ethanol extract of Brazilian propolis), was obtained from a commercial supplier (ChatBlanc inc., Tokyo, Japan). Lyophilized CB Propolis is equivalent to 18.5 mg propolis per 100 ml. In this study propolis was diluted in dimethysulfoxide (DMSO) and filtered with a sterile filter prior to use, and then added at the appropriate final concentrations to cultures of U937 cells. Control cells were treated with the same amount of vehicle alone. The final DMSO concentrations never exceeded 0.5% (v/v). In this condition, we confirmed that apoptosis was not observed in U937 cells. Z-Asp-CH 2 -DCB (a wide-spectrum caspase inhibitor) was purchased from Peptide Institute (Osaka, Japan). The cells were treated with 100 mM inhibitor for 1 h before the treatment with propolis. [ Cell Lines and Cell Culture To examine the effects of propolis on cell proliferation, U937 human histiocytic lymphoma cells were obtained from the Japanese Research Resources Bank, Tokyo, Japan. The cells (4ϫ10 6 cells/ml) were grown in RPMI 1640 medium (Iwaki Co., Ltd, Tokyo) supplemented with 100 units/ml of penicillin, 100 mg/ml streptomycin and 10% heat-inactivated fetal bovine serum at 37°C under a humidified 95% air 5% CO 2 atmosphere, and passaged every 7 d. U937 cells had a doubling time of about 24-30 h under these conditions.Cell Proliferation Experiments Cells were inoculated at a d...
