Ethnopharmacological relevance: Tabebuia pallida (Lindl.) Miers (T. pallida) is a well-known native Caribbean medicinal plant. The leaves and barks of T. pallida are used as traditional medicine in the form of herbal or medicinal tea to manage cancer, fever, and pain. Moreover, extracts from the leaves of T. pallida showed anticancer activity. However, the chemical profile and mechanism of anticancer activity of T. pallida leaves (TPL), stem bark (TPSB), root bark (TPRB) and flowers (TPF) remain unexplored.
Aim of the study: The present study was designed to explore the regulation of apoptosis by T. pallida using Ehrlich Ascites Carcinoma (EAC) cultured cells and an EAC mouse model. LC-ESI-MS/MS was used for compositional analysis of T. pallida extracts.
Materials and methods: Dried and powdered TPL, TPSB, TPRB and TPF were extracted with 80% methanol. Using cultured EAC cells and EAC-bearing mice with and without these extracts, anticancer activities were studied by assessing cytotoxicity and tumor cell growth inhibition, changes in life span of mice, and hematological and biochemical parameters. Apoptosis was analyzed by microscopy and expression of selected apoptosis-related genes (Bcl-2, Bcl-xL, NFκ-B, PARP-1, p53, Bax, caspase-3 and -8) using RT-PCR. LC-ESI-MS analysis was performed to identify the major compounds from active extracts. Computer aided analyses was undertaken to sort out the best-fit phytoconstituent of total ten isolated compounds of this plant for antioxidant and anticancer activity.
Results: In EAC mice compared with untreated controls, the TPL extract exhibited the highest cancer cell toxicity with significant tumor cell growth inhibition (p < 0.001), reduced ascites by body weight (p < 0.01), increased the life span (p < 0.001), normalized blood parameters (RBC/WBC counts), and increased the levels of superoxide dismutase and catalase. TPL-treated EAC cells showed increased apoptotic characteristics of membrane blebbing, chromatin condensation and nuclear fragmentation, and caspase-3 activation, compared with untreated EAC cells. Moreover, annexin V-FITC and propidium iodide signals were greatly enhanced in response to TPL treatment, indicating apoptosis induction. Pro- and anti-apoptotic signaling after TPL treatment demonstrated up-regulated p53, Bax and PARP-1, and down-regulated NFκ-B, Bcl-2 and Bcl-xL expression, suggesting that TPL shifts the balance of pro- and anti-apoptotic genes towards cell death. LC-ESI-MS data of TPL showed a mixture of glycosides, lapachol, and quercetin antioxidant and its derivatives that were significantly linked to cancer cell targets. The compound, pelargonidin-3-O-glucoside was found to be most effective in computer aided models.
Conclusions: In conclusion, the TPL extract of T. pallida possesses significant anticancer activity. The tumor suppressive mechanism is due to apoptosis induced by activation of antioxidant enzymes and caspases and mediated by a change in the balance of pro- and anti-apoptotic genes that promotes cell death.
Keywords: Apoptosis; Caspases; EAC cells; LC-MS; NFκ-B; Tabebuia pallida; p53.
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