Portuguese propolis: Genotoxic, phytotoxic and protective effects against oxidative stress

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Propolis is a waxy mixture produced by bees from various plant sources with a diverse chemical composition. Although associated with varied biological activities, like antioxidant, antimicrobial, anti-inflammatory, anti-tumoral using animal and cell models, reports on genotoxicity are very scarce, and on phytotoxicity are absent to our knowledge. In this study Portuguese propolis samples from different apiaries collected in different years were extracted with ethanol (EE) and n-hexane (HE) and tested using yeast (Saccharomyces cerevisiae) and in vitro plants (Linum usitatissimum) as models. Toxicity was assessed by viability assays (drop test) in yeast and by plant growth analysis. Mechanisms of cytotoxicity were investigated by flow cytometry with rhodamine 123 [1] and genotoxicity by the comet assay [2] in the unicellular model. The plant model was used to evaluate effects at the developmental level as well as in the photosynthetic function by pulse amplitude modulated fluorometry [3]. Antioxidant properties were studied in yeast by flow cytometry with the redox-sensitive fluorochrome dichlorofluorescein diacetate [4], and in plants assessing the protective potential against fotooxidative damage induced under highlight conditions. Results showed that some EE exhibit high toxicity in both models, decreasing yeast viability and mitochondrial membrane potential, increasing genotoxicity and affecting significantly early plant growth and photosynthetic competence in a dose-dependent manner. At 200 µg/ml P10 EE caused a DNA damage similar to 10 mM H2O2 treatment. At 50 µg/ml root growth was inhibited up to 20% of the control. Some EE also decrease intracellular oxidation induced by H2O2, and avoid chlorophyll photobleaching under photooxidative conditions. Globally our data support the antioxidant properties revealed by propolis worldwide but also underline the strong toxicity in different cellular models, suggesting common mechanisms of action among eukaryotes.