Advances in the Structural Characterization of Saponins from Pereskia grandifolia Haw. Leaves: Chemical Modifications and Mass Spectrometry Insights, and the Cytotoxic Activities of a Rich Saponin Fraction
Eduarda C. Amaral, Diogo H. Kita, Otávio B. O. Martins, Ligia T. Burigo, Alan de A. Veiga, Francislaine A. R. Lívero, Arisa N. Higashijima, Gustavo da Silva Ratti, Simony R. B. Rosa, Ezilda Jacomassi, Lucas Pires Guarnier, João T. Ribeiro-Paes, Bassam F. Mogharbel, Cintia de O. Soares, Katherine A. T. de Carvalho, Lauro M. de SouzaBackground/Objectives: Pereskia grandifolia Haw. is a plant native to Central and South America and belongs to the Cactaceae family, and it is valued in the human diet for its nutritional value. Recently, this species was reported to contain a variety of saponins, but structural details remain limited because of their number and complexity. Saponins exhibit pharmacological properties, making their characterization useful. Methods: Comprehensive mass spectrometry analysis, combined with chemical methylation of the entire saponins, provided critical information on the distribution of sugar moieties associated with the monosaccharides and the aglycone. We also assessed cellular antioxidant capacity, cytotoxicity, and antiproliferative effects against breast tumor cell lines by staining for Ki-67, Annexin V, and 7AAD. Results: Fifteen saponins were identified with oleanolic and ursolic acids. Oligosaccharides were formed by glucuronic acid, with additional glucose units attached to the glucuronic acid or the aglycone, which had not been reported previously. This fraction showed cytotoxic and antiproliferative effects against various tumor cell lines, with the best IC50 at 90 µg·mL−1, and reduced chemotherapy-induced reactive oxygen species (ROS) levels. Whereas cytotoxic effects in most cell lines involved necrosis, MCF-7 exhibited antiproliferative and cytostatic effects, with apoptosis as the main death pathway. Conclusions: The methods used here enabled a comprehensive evaluation of saponins, eliminating the need for extensive purification. Even in a mixture, methylation provided critical structural details that enabled the characterization of different structures, including several isomers. The anti-ROS activity observed in this extract may be associated with modulating cytotoxic responses by preventing oxidative cell damage.