Effects of a Propolis Extract on the Viability of and Levels of Cytoskeletal and Regulatory Proteins in Rat Brain Astrocytes: an In Vitro Study

A potential for the use of propolis in preventive and therapeutic purposes has been acknowledged, but little attention has been paid to estimation of possible propolis cytotoxicity with respect to astrocytes. We tried to estimate how a propolis ethanol extract (PEE) affects rat brain astrocytes in vitro and also to uncover crucial molecular targets of the PEE action. Primary astrocytes were exposed to PEE in doses of 10, 25, or 100 μg/ml for 24 h, and then the cell viability was monitored by MTT assay. Levels of glial fibrillary acidic protein (GFAP), transcriptional nuclear factor-κB (NF-κB), poly(ADPribose) polymerase (PARP), and angiostatins were measured using Western blot to identify the molecular mechanisms underlying cell responses to PEE. The PEE treatment exerted a dose-dependent cytotoxic effect on cultured astrocytes. The PEE modulated astrocyte signaling pathways through inducing the expression of NF-κB and PARP. At the same time, the PEE stimulated GFAP synthesis and fibrillogenesis, which was indicative for activation of astrocytes preceding their suppression. The PEE significantly increased the production of angiostatin isoforms by astrocytes, thus contributing to an antiangiogenic potential of these cells. In summary, our results indicated that exposure to the PEE exerts certain cytotoxic effects on astrocytes in a dose-dependent manner; these effects are realized through modulation of cytoskeleton rearrangements and pro-apoptotic signaling pathways. A widely available, safe, and inexpensive substance, propolis, and its components and derivatives may be used in the prevention and treatment of neuronal impairments, including malignant tumors and neurodegenerative disorders associated with excessive astrocytic activation.

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