The Study of Chemical Profile and Antioxidant Properties of Poplar-Type Polish Propolis Considering Local Flora Diversity in Relation to Antibacterial and Anticancer Activities in Human Breast Cancer Cells

Abstract

Nine samples of ethanolic extracts of poplar-type propolis (EEP) originated from South-Eastern Poland were analyzed in terms of the diversity of the flora around the apiary. The mineral composition, antioxidant properties, polyphenolic profile (HPTLC), and main polyphenolic constituents (HPLC-DAD) were determined. Only minor differences in chemical composition and antioxidant capacity between tested EEPs were found regardless of their botanical origin. However, the biological activity of the EEPs was more diversified. The tested EEPs showed stronger antibacterial activity against Gram-negative bacteria (Escherichia coli) compared to Gram-positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis). Staphylococci biofilm inhibition occurred as a result of exposure to the action of four out of nine EEPs (P1-P4). Due to the various compositions of individual EEPs, a different MCF-7 cellular response was observed according to inhibition of cells migration and proliferation. Almost every sample inhibited the migration of breast cancer cells at a low concentration (0.04 µg/mL) of propolis. Even at the lowest concentration (0.02 µg/mL), each EEP inhibited the proliferation of MCF-7 cells, however, the level of inhibition varied between samples.

Keywords: HPTLC; antibacterial effect; anticancer activity; antioxidants; polyphenols; propolis.

Figure 1

Images of HPTLC polyphenolic profile development after p-anisaldehyde derivatization, in visible light (A) and 366 nm UV light (B). Track 10 for the mixture of 3-components, in order of increasing Rf: CA—caffeic acid, p-CouA—p-coumaric acid, Ch—chrysin. P1–P9—propolis samples.

Figure 2

Percentage of the flavonoid fraction in the total content of phenolic compounds and the ratio of quantified flavonoids to phenolic acids (HPLC method). P1–P9—propolis samples.

Figure 3

Inhibition of MCF-7 cells migration after incubation with P1–P9 propolis samples determined with the scratch test. Data are presented as means ± SD. P1–P9—propolis samples.

Figure 4

Selected microscopic images of the MCF-7 cell migration scratch assay as a result of 12 and 24 h of exposure to EEPs of P7 and P8 samples.

Figure 5

Inhibitory effects against MCF-7 cells at each concentration of 9 different EEP samples after 24 h of incubation. The color reflects the concentration of the sample (from lightest to darkest): 0.04, 0.08, 0.2, 0.4, 0.8 µg/mL. Data are presented as means ± SD. P1–P9—propolis samples.