Bioactive phytochemicals from Libyan medicinal plants : Cynara cyrenaica Maire and Weill and Cyclamen rohlfsianum Aschers

  • Tahani M Mohamed El Tomi

Student thesis: Doctoral Thesis

Abstract

Medicinal plants have a long history in the treatment of diseases. Studies on phytochemicals from medicinal plants have continued to increase due to their importance in the search for new drugs. The El-Jabal El-Akhdar region (Green Mountain) of Libya has a high diversity of medicinal plants which are presently poorly studied. This dissertation describes studies on Cynara cyrenaica and Cyclamen rohlfsianum, collected from the region, for phytochemical, anticancer and antidiabetic evaluation. The phytochemical evaluation revealed one saponin 3-O-{β-D-xylopyranosyl-(12)-β-D-glucopyranosyl-(14)-[β-D-glucopyranosyl-(12)]-α-L-arabinopyranosyl}-cyclamiretin A (CY1) isolated from C. rohlfsianum. Thirteen compounds were isolated from C. cyrenaica, including two identified as novel sesquiterpene lactones named 3β-hydroxy-8α-[(S)-4-hydroxy-3- methylbutanyloxy]-guaian-4(15), 10(14), 11(13)-trien-1α, 5α, 7α, 6βH-12, 6-olide (CC12) and 11, 13 epoxy-guaian-4(15), 10(14)-dien-1α, 5α, 7α, 6βH-12, 6-olide-3-yl acetate (CC13). The other compounds were taraxasterol, pseudotaraxasterol, ll,13-epoxysolstitialin (CC5), apigenin, luteolin-7-O-β-D-glucopyranoside, luteolin, catechin 7-O-gallate, ferulic acid, 1, 3-dicaffeoylquinic acid, daucosterol and 1-monoacetyl glycerol. A preliminary in vitro antidiabetic assessment of all crude solvent extracts and most of the isolated compounds was carried out using α-glucosidase, protein tyrosine phosphatase 1B (PTP1B) and α-amylase inhibition tests. For α-glucosidase, only catechin 7-O-gallate from C. cyrenaica was found to be active with significant (p <0.001) inhibition and produced concentration-dependent inhibition with an IC50 value of 3.94 ± 1.1μM. For the C. rohlfsianum tuber, the crude methanol extract and CY1 isolated from this extract produced marked inhibitory activity on α-glucosidase with IC50 values of 3.46 ± 1.13μg/ml and 5.53 ± 1.1μM, respectively.For PTP1B assay only luteolin from C. cyrenaica was found to be significantly (p <0.001) active and showed dose-dependent inhibition activity with an IC50 value of 15.94 ± 1.12μM. In an α-amylase assay, no inhibition of the enzyme was produced by both plants. These findings provide some scientific support for the traditional use of this plant as an anti-diabetic. The crude solvent extracts and some of the isolated compounds were also screened in vitro for cytotoxicity against human cancer cell lines: A375 (malignant melanoma), PANC-1 (pancreatic carcinoma), and HeLa (cervical cancer) in comparison with a non-cancer PNT2 cell line (prostate cell line) using an AlamarBlue® assay. Among the crude solvent extracts tested, the n-hexane and ethyl acetate extract of C. cyrenaica flower heads showed inhibition of metabolic activity on all the cell lines, including the PNT2 cells, but those of the ethyl acetate extract of the root, leaf and stem were the most potent against PANC-1 cells with IC50 values of 2.73 ± 1.18, 0.004 ± 1.02 and 1.40 ± 1.87μg/ml, respectively and showed inhibition effect on PNT2 cells with different ranges of IC50. For the ethyl acetate extracts of C. cyrenaica root and stem this effect could be linked in part to the presence of sesquiterpene lactones (CC5, CC12 and C13). Furthermore, the n-hexane extract of C. cyrenaica leaf also showed inhibitory metabolic activity in HeLa and PANC-1 cells at 25μg/ml and showed inhibition effect on PNT2 cells with IC50 value of 10.71 ± 1.30μg/ml. For the C. rohlfsianum tuber, the only inhibition was observed with the methanol extract on all the cell lines, including the PNT2 cells with an IC50 value of 3.16 ± 1.08μg/ml for PNT2 and 6.35 ± 1.09, 42.37 ± 1.13 and 4.19 ± 1.11μg/ml for A375, HeLa and PANC-1, respectively. Among the screened compounds, taraxasterol showed selective activity against HeLa cells with no toxic effect on normal cells.While luteolin, ll, 13-epoxysolstitialin, CY1 and CC12 were
Date of Award1 May 2017
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorValerie Ferro (Supervisor) & (Supervisor)

Cite this