The genus Rhododendron is one of the 20 most species-rich plant genera. The Rhododendronpark Bremen harbors the second largest collection of species and hybrids worldwide. Our collaborative projects with research groups from Jacobs University, the University of Oldenburg, and the Rhododendronpark Bremen revealed the genus Rhododendron offers access to an overwhelming range of bioactive substances. Extracts from approx. 200 Rhododendron species have been tested qualitatively and quantitatively regarding their antimicrobial, cytotoxic and antitumor potentials. In particular, the cytotoxic effects exerted by Rhododendron-derived leaf extracts with antimicrobial activities were examined for two types of mammalian target cells: intestinal epithelial and skin cells. Using a combination of five different cell and molecular biological assays, plasma membrane integrity, cell viability and proliferation rates, cellular metabolism, cytoskeletal architecture, and initiation of cell death pathways were analyzed. Out of 12 Rhododendron leaf extracts with significant antimicrobial effects, extracts from two species, only, were considered harmless to both cell types with respect to any of the tests, while extracts from another three species were safe for one of the cell types cultured but not the other. These results allowed concluding that the combination of bioactive compounds within extracts varies from species to species thus prompting systematic approaches to dissect desired from unwanted bioactivities in our future concerted approach.
Supported by Stiftung Bremer Rhododendronpark, 2012 – 2013, Groups of Matthias Ullrich (JU), Klaudia Brix (JU), Nikolai Kuhnert (JU), and Dirk Albach (Univ. Oldenburg), “Forschung an Rhododendron-Arten im Rhododendron-Park Bremen”
- Hakeem Said, I.H., A. Rezk, I. Hussain, A. Grimbs, A. Shrestha, H. Schepker, K. Brix, M.S. Ullrich, and N. Kuhnert (2017). Metabolome comparison of bioactive and inactibe Rhododendron extracts and identification of an antibacterial cannabinoid from Rhododendron collettianum. Phytochemical Analysis, in production. DOI:10.1002/pca.2694
- Grimbs, A., A. Shrestha, A.S.D. Rezk, S. Grimbs, I. Hakeem Said, H. Schepker, M.-T. Hütt, D.C. Albach, K. Brix, N. Kuhnert, and M.S. Ullrich (2017). Bioactivity in Rhododendron: A systemic analysis of antimicrobial and cytotoxic activities and their phylogenetic and phytochemical origins. Frontiers in Plant Science, 8, Article 551. Doi: 10.3389/fpls.2017.00551
- Elsadig Karar, M.G., L. Quiet, A. Rezk, R. Jaiswal, M. Rehders, M.S. Ullrich, K. Brix, and N. Kuhnert (2016). Phenolic profile and in vitro assessment of cytotoxicity and antibacterial activity of Ziziphus spina-christi leaf extracts. Med. Chem. (Los Angeles) 6, 143-156. doi: 10.4172/2161-0444.1000339. http://www.omicsonline.org/open-access/phenolic-profile-and-in-vitro-assessment-of-cytotoxicity-and-antibacterialactivity-of-ziziphus-spinachristi-leaf-extracts-2161-0444-1000339.php?aid=70331
- Rezk, A., A. Al-Hashimi, W. John, H. Schepker, M.S. Ullrich, and K. Brix (2015b). Assessment of cytotoxicity exerted by leaf extracts from plants of the genus Rhododendron towards epidermal keratinocytes and intestine epithelial cells. BMC Complement Altern Med. 15:364. doi: 10.1186/s12906-015-0860-8
- Rezk, A., J. Nolzen, H. Schepker, D.C. Albach, K. Brix, and M.S. Ullrich (2015a). Phylogenetic spectrum and analysis of antibacterial activities of leaf extracts from plants of the genus Rhododendron. BMC Complementary & Alternative Medicine 15:67. DOI 10.1186/s12906-015-0596-5.