Phytochemical and cytotoxicity studies on Arbutus pavarii, Asphodelus aestivus, Juniperus phoenicea and Ruta chalepensis growing in Libya

Abstract

The work incorporates systematic bioassay-guided phytochemical and cytotoxicity/anticancer studies on four selected medicinal plants from the Libyan flora. Based on information on their traditional medicinal uses and the literature survey, Juniperus phoenicea L. (Fam: Cupressaceae), Asphodelus aestivus Brot. (Fam: Asphodelaceae), Ruta chalepensis. L (Fam: Rutaceae) and Arbutus pavarii Pampan. (Fam: Ericaceae) have been selected for investigation in the current endeavour. The four plants are well-known Libyan medicinal plants, which have been used in Libyan traditional medicine for the treatment of various human ailments, including both tumours and cancers. The cytotoxic activity of the n-hexane, dichloromethane (DCM) and methanol (MeOH) extracts of these plants were assessed against five human tumour cell lines: urinary bladder cancer [EJ-138], liver hepatocellular carcinoma [HEPG2], lung cancer [A549], breast cancer [MCF7] and prostate cancer [PC3] cell lines. The cytotoxicity at different concentrations of these extracts (0, 0.8, 4, 20, 100 and 500 µg/mL) was evaluated by the MTT assay. The four plants showed notable cytotoxicity against the five aforementioned human tumour cell lines with different selectivity indexes on prostate cancer cells. Accordingly, the cytotoxic effect of various chromatographic fractions from the different extracts of these plants at different concentrations (0, 0.4, 2, 10, 50 and 250 µg/mL) revealed different cytotoxic properties. Twenty-nine compounds were isolated from different fractions of these plants: three bioflavonoids, amentoflavone (25), cupressoflavone (24) and sumaflavone (76); four diterpenes. 13-epi-cupressic acid (42), imbricatholic acid (41), 3-hydroxy sandaracopimaric acid (44) and dehydroabietic acid (46), one alkanol (heptacosanol) and two lignans, deoxypodophyllotoxin (29) and β-peltatin methyl ether (28)] from J. phoenicea leaves; one flavonoid, luteolin (22), four anthraquinones [aleo-emodin (13), chrysphanol anthrone (79), 10, 10`chrysphanol bianthrone (80) and C-α-rhamnopyranosyl bianthracene-9, 9’, 10 (10'H)-trione glycoside (81) and p-hydroxy-phenethyl trans-ferulate (82) from A. aestivus leaves and tubers; three alkaloids, kokusaginine (61), graveoline (60), and 4-hydroxy-2-nonyl-quinoline (85), three coumarins, bergapten (63), chalepin (64) and chalepensin (65), one alkane, tetradecane, two flavonoid glycosides, rutin (52) and methoxy rutin (83) and 3``, 6`-disinapoylsucrose (84) from R. chalepensis aerial parts; one hydroquinone--D-glucopyranoside, arbutin (53) and two pentacyclic triterpenes, methyl betulinate (89) and ursolic acid (88) from A. pavarii leaves. Twenty-three isolated compounds were tested for their cytotoxicity against the most sensitive cancer cell lines. Eight compounds revealed good cytotoxic activity: cupressoflavone (24), sumaflavone (76), epicupressic acid (42), luteolin (22), chalepin (64) and 4-hydroxy-2-nonyl-quinoline (85) were cytotoxic against the A549 with IC50 values of 65, 77, 159, 76.9, 92 and 97.6 µM, respectively, whilst, compound 64 showed toxicity also against EJ138 with an IC50 value of 117 µM. C-α-rhamnopyranosyl bianthracene-9, 9’, 10 (10'H)-trione (81) and ursolic acid (88) were toxic against the prostate cancer cell line with IC50 values of 62 µM and 8.22 µM, respectively. The study findings also indicated that compounds 24, 64 and 88-induced cell death might involve the plasma membrane damage resulting in the release of LDH enzyme from the necrotic cells.