Antimicrobial activity and nutraceutical potential of Tuscan bee-pollens on oxidative and endoplasmic reticulum stress in different cell-based models

Bee pollen is an apiary product of great interest owing to its high nutritional and therapeutic properties and represents an important source of energy, bioactive compounds, and proteins for human nutrition¹. In a previous study, we evaluated the botanical origin, phytochemical profile, and free-radical scavenging activity of polyfloral Tuscan bee pollen separated by color into three botanical families, mainly Castanea, Rubus, and Cistus².

This study aimed to assess the antioxidant activity and the anti-hemolytic effects of Castanea, Rubus, and Cistus bee pollen on oxidized human erythrocytes through the CAA-RBC (Cellular Antioxidant Activity in Red Blood Cells) and hemolysis tests. Besides, we analyzed the antimicrobial potential of each sample on three Gram-negative bacteria (Escherichia coli, Salmonella enterica ser. Typhimurium, and Enterobacter aerogenes) and two Gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus) by evaluating the minimal inhibitory concentration (MIC). Finally, the effect of Castanea bee pollen, showing the highest phytochemical content, was analyzed on human microvascular endothelial cells (HMEC-1) exposed to thapsigargin, a plant-derived sesquiterpene lactone used to induce endoplasmic reticulum stress (ER-stress).

Our results showed good biological activities of all bee pollen samples that, under oxidative conditions, significantly improved the erythrocytes antioxidant activity also protecting them from the cell lysis. Our results demonstrated comparable Castanea and Cistus anti-hemolytic activities, with higher % hemolysis inhibition than Rubus bee pollen at similar doses. Moreover, all bee pollen extracts exerted antimicrobial activity with different selectivity among tested microorganisms and MIC values ranging from 5 to 10 mg/ml. Finally, our findings showed that thapsigargin treatment did not affect the HMEC-1 viability, while increased the intracellular ROS production, and up-regulated the expression of factors involved in the ER stress and inflammatory pathway (CHOP, IL-6, COX-2, and ICAM-1). Conversely, Castanea bee pollen was effective in reducing the CHOP, IL-6, COX-2, and ICAM-1 overexpression, as well the oxidation process arising from thapsigargin treatment, with maximum protective effect at 10µg/ml.

In conclusion, polyfloral Tuscan bee pollen, mainly Castanea and Cistus species, represents a good natural antibacterial and a potential nutraceutical product useful in the prevention of free radical and ER stress-associated diseases.

_References

_{1. Abouda Z., Zerdani I., Kalalou I., Faid M., Ahami M.T. The antibacterial activity of Moroccan bee bread and bee-pollen (Fresh and Dried) against pathogenic bacteria. Res J Microbiol. 2011, 6, 376-384.}

_{2. Gabriele M, Parri E, Felicioli A, Sagona S, Pozzo L, Biondi C, Domenici V, Pucci L. Phytochemical composition and antioxidant activity of Tuscan bee pollen of different botanic origins. Ital J Food Sci. 2015, 27, 248-59.}